Intralesional Triamcinolone injection (5 to 10 believe that keloids never undergo malignant • Postoperative pressure therapy mg biweekly upto 10 injections) produces change) 50mg azathioprine mastercard spasms right side of stomach. Histologically epi dermis such as fbrous tissue discount azathioprine 50mg visa spasms bladder, neural tissue purchase azathioprine with visa muscle relaxant cyclobenzaprine high, dermis is composed of several layers viz. Histiocytes – Histiocytoma, malignant keratinocyte, melanocytes, and Langerhans • Malignant melanoma. Keratinocytesare arranged in several layers of polygonal cells forming the stratum spinosum. Melanocytes are situated at the junction of epidermis and dermis and derived from the neural crest cells. Langerhans cells or dendritic cells of Langerhans belong to the mononuclear phago cytic system and are located in the stratum spinosum. It also con tains blood vessels in fne plexuses, intricate network of nerve fbers and sensory nerve endings for pain, touch and temperature. Fibrous tissue – Fibroma, fbrosarcoma, The size varies from a few millimeters to etc. From sweat glands (Eccrine tumors, treatment apocrine tumors, sweat gland Papillomas are usually excised for cosmetic carcinoma). Another nomenclature is tear cancer The epidermis shows hyperkeratosis because it is commonly found along the (Tickening of horny layer), acanthosis Papilloma of the skin region on the face when tears roll down. Bowen’s disease is the common variety of Squamous Cell Papilloma infammatory cells and benign fbrovas squamous cell carcinoma in situ involving Tere are four varieties of such papilloma: cular tissue. Etiology - Mostly occur on sun exposed Grossly, there is irregular erythematous patch illoma which probably arises from virus skin, especially face, or afer arsenic expo with sharp outline and scaling or crusting. It also occurs in two rare inherited the penis, it is called erythroplasia of Queyrat. Infective wart may regress by itself but disorders viz Xeroderma pigmentosa and Squamous cell carcinoma develops in 10 may recur afer removal. Prognosis - May infltrate deeply but may be difcult to diferentiate from a rarely metastasize. Sof papilloma - Which is ofen seen on • Edge of the ulcer - Raised and rounded producing microscopically or macroscopi the eyelids of elderly people. Keratin horns, also seen in the elderly peo the growth spreads, the shape becomes from epithelial surfaces ((Fig. It may arise either from epidermis or from • Floor - First superfcial, then deep and mucous membrane and always contains a Basal Cell Papilloma even proceeds upto bone. The various examples Tese commonly occur on the face, trunk, less pronounced or barely perceptible are: arms and arm pits. Excision should be done with a clear sites Presence of cell nests in a squamous cell healthy margin of 35 mm or more around a. Mucous surface covered by stratifed ated and rapidly growing tumor, sensitive Disadvantage of the above methods squamous epithelium, e. Blood spread occurs • Edge of the ulcer - Rolled out and only in very advanced cases. Indications of surgery are as follows: In case of skin, it is the prickle cell layer from • Base - Indurated and may be fxed to 1. It may arise de novo – in a previously nor lium which invade the subjacent connec – For lesions in the scalp. It cures 80 Besides the skin, naevi can occur in the nail • Persistent itching, bleeding, increase in percent of early lesions. If scopically if there is hyperchromasia, lymph nodes are hard and fxed palliative radi Pathology mitotic fgures, pleomorphism and sub otherapy is given. Nevus at a site prone to repeated trauma, basal layer of epidermis and thought to be junctional nevus. Macroscopical Any excised naevus should be sent for his Melanophores are phagocytes. Microscopical Incidence • Junctional naevi are composed of The incidence of malignant melanoma is Role of Hormone groups of melanocytes appearing as increasing every decade, highest being in Synthesis of melanin is hormonedependent. Sex hormones • In intradermal nevi, the nevus cells the rest from the preexisting mole, e. Estrogen and Progesterone in female are limited to the dermis and may be tional nevus, compound nevus, etc. Malignant activity afer puberty 20 percent of • Types: (i) Two principal types viz. The following are the evidences of malignant palpable and nodule may develop within The naevi can occur anywhere in the skin. Spread Histological classification (Clark’s Local - Horizontally in the epidermis and level of invasion) vertically into the dermis. The deep fascia Depends on the anatomic level of invasion acts as a strong barrier. Lymphatic spread - By emboli to regional Classification by tumor thickness lymph nodes and by permeation of lymphatic (Breslow): channels giving rise to secondary deposits or Tis classifcation is more important for satellite nodules between the primary growth fig. It is the most and Breslow’s tumor thickness measurement Depends on the depth of invasion (Clarke malignant type. Ulcerated lesions may Arm, Nerve, Scalp) region melanoma has a • Acral lentiginous melanoma – a variety be relatively thin, yet have a poor prognosis, poor prognosis. Also at present there are no methods of Clark’s level Description 5 year survival of invasion establishing metastasis. Level 1 Epidermal involvement only 100% Level 2 Papillary dermis only is involved 90-100% Level 3 Involves the junction of papillary and 80-90% reticular dermis Level 4 Tumor extends to reticular dermis 60-70% Level 5 Subcutaneous fat is involved 15-30% Table 12. It is painless as scar does not It can be painful if it infiltrates the • Difuse telangiectasia, usually seen on the contain nerves. Lymphatic metastasis does not occur Lymphatic metastasis is the chief as they are destroyed in a scar. Definition Features: Treatment Low grade epidermoid or squamous cell • Tis produces swelling which is com a. Treatment of the lesion: carcinoma arising from the epithelium pressible and consists of immature vascu i. Surgical excision is the treatment of covering the scar tissue or keloid, is called lar tissue. Operative - Excision with or without with the lesion but it is not necessary treatment skin grafing. Isolated limb perfusion: Tis is a swelling due to congenital malfor Indications: mation of blood vessels. It is efective in reducing the Types lesion size and on occasion, healing them • Strawberry angioma (Syn. Neurolipoma-Mixture of nervous and the diagnostic sign, when the swelling is there are ischemic ulcers due to compara adipose tissue, ofen painful. Nevolipoma - Mentioned above, in cav • Sof cystic, fuctuant but transillumina ernous hemangeoma.
It is associated with headache azathioprine 50 mg with mastercard muscle relaxant anxiety, palpita- Treatment tions and diaphoresis which constitute Surgical removal is the only satisfactory Pathology the ‘classic triad’ of pheochromocytomas order azathioprine 50 mg overnight delivery muscle relaxer 7767. Preoperative use of alpha and beta Macroscopically the tumor usually attains a Symptoms such as nausea buy 50 mg azathioprine visa muscle relaxant used in dentistry, vomiting, par- adrenergic blocking agents, meticulous intra- huge size like the Wilms’ tumor. The surface esthesias, anxiety, fushing, chest pain and operative monitoring and modern anesthesia is nodular with a maroon color and there are shortness of breath are nonspecifc and has made surgery safe. Cardiovascular complications such as Preoperative Preparation small round cells which are highly immature myocardial infarction and cerebrovascu- It should begin 48 hours before surgery or and undiferentiated type. Tese symptoms may be incited by a range antagonist, phenoxybenzamine 20 to 40 mg frequently. Persistent hypertension occurs in 50 per- never be used without a prior alpha blockade in children, more than 80 percent occurring cent of cases. Sometimes an infant of paroxysmal increase may occur from may be born with a neuroblastoma. The common medications used for intra- In almost all cases there is pallor, weight 6. Pheochromocytoma should be suspected operative blood pressure control include nitro- loss and anorexia. More than 60 percent cases in patients with malignant hypertension prusside, nitroglycerin and phentolamine. During simultaneous handling of bilateral of diagnosis like bone pain, cutaneous meta- tumors a hydrocortisone drip is required. Tumor calcifcation seen inhibited by the negative feedback efects of • Aspiration of bone marrow may show on plain X-ray is a common fnding. Treatment steroid hormones produced by the adrenal Under physiological conditions, about 75 • Early cases respond very well to surgical cortex. The adrenal cortex contains rela- percent of plasma cortisol is bound to cortisol excision. Conversion of cholesteryl cent is bound to plasma albumin and about receive initial chemotherapy with cyclo- ester to free cholesterol is a necessary step in 10 percent is unbound. Mineralocorticoids Tey directly stimulate intrahepatic synthe- Tese are concerned in the maintenance of Ganglioneuroma sis of glucose from noncarbohydrate sources water and electrolyte balance. It causes the sympathetic nervous system and repro- Cortisol or hydrocortisone is the chief of sodium retention by the kidneys and expansion duces ganglion cells of adult type. It is a these hormones and is responsible for 95 per- of the extracellular fuid volume. The secretion benign tumor and least harmful among the cent of all glucocorticoid activity. The remainder depends mainly on in adults and usually presents with pressure enhanced under stress and trauma and is the renin – angiotensin system. Substitution cortisone ther- renal arteriole close to the macula densa in occurring between 30 to 40 years. Sodium Oligomenorrhea and virilism occur in retention and expansion of blood volume by females; while males have gynecomastia and Primary Hyperaldosteronism aldosterone turns of the production of renin. Pathological In this condition, there is excess aldos- aldosterone production can be subdivided fractures may occur. About 90 percent of patients with primary Plasma Cortisol Level • Hypovolemia from any cause will afect aldosteronism have benign solitary adreno- the release of renin which ultimately Nine am and 9 pm plasma cortisol estima- cortical adenoma (Conn’s syndrome). Free Rarely primary aldosteronism is produced cortisol level in urine (> 100mg/24hrs) is the by adrenocortical carcinoma. Suppression Test microscopically there are large lipid laden Excess of androgens will produce virilism Tis test may distinguish between Cushing’s cells arranged in cords and acini. Clinical Features Tis test is carried out by administering • It is twice common in women aged 30 to Cushing’s Syndrome 2 mg q i d of dexamethasone for 2 days. Suppressed levels are seen in patients with • Muscle weakness, polydipsia, fatigue and Definition pituitary dependent Cushing’s disease but not nocturnal polyuria occur due to excessive In this syndrome, an excessive secretion of in a patient with adrenal tumor or an ectopic potassium loss. The condition is rare in incidentaloma Surgery is reserved for the refractory cases males and virilism attracts little attention. Functioning lesions: The congenital infantile variety is by far formed for an unrelated indication. Tis is an autosomal dence increases with age and in patients with – Sex steroid producing adenoma recessive disorder caused by defciency of hypertension. Malignant enzymes, mostly 21 hydroxylase (95%) in Nonfunctioning adrenocortical adeno- – Adrenocortical cancer the synthetic pathways of cortisol. Plasma electrolytes, aldosterone and renin In childhood and adult types, the com- Investigations to rule out an aldosteronoma. The adult or growing female who would beneft from adrenalalectomy that the most likely adrenal abnormality will be metastasis. Incidentaloma of 4 cm or more in diame- ter carry an increased risk of malignancy. Patients with functional tumors as deter- mined by biochemical testing or with obvious malignant lesion, should undergo adrenalectomy. A unilateral nonfunctioning adrenal mass > 4 cm in diameter is an indication for adrenalectomy. Metastasis - Resection of solitary adrenal metastases of nonadrenal cancers from lungs or kidney has been demonstrated to lead to prolonged patient survival. Suspected adrenal metastases may also be resected for diagnosis or for palliation if Fig. Any underlying infection is treated aggres- processes that destroy the adrenal cortex, e. Tuberculosis, metastatic, malignancy (breast, ing, abdominal pain, fever, hypoglycemia Patients with chronic adrenal insuf- lung), Autoimmune (Polyglandular autoim- and electrolyte imbalance. It may also result ciency are treated with maintenance oral mune disease), Hemorrhage (Spontaneous, from sudden deterioration of chronic adrenal hydrocortisone in divided doses and fudro- e. Tey must be educated with and secondary to stress trauma, infections, Symptoms of chronic adrenal insufciency regard to their life long need for glucocorti- coagulopathy, etc. A strong clinical steroid cover when subjected to severe stress, pituitary hemorrhage (Sheehan’s syndrome), suspicion is enough to start the treatment. In various places Such ulcerated surface becomes covered on to rest pain and gangrene. Tese emboli may tion to the ischemia early are loss of hair, intermittent claudication, rest pain and gan- lodge anywhere, either near the athero- dry, wrinkled and atrophied skin, cessation grene, in the heart it causes angina pectoris sclerotic artery or some distance away of sweating and sebaceous secretion, and and myocardial infarction, in the brain, tran- from it. Arterial occlusion is of two types – acute and pain, paresis, paresthesia, pallor and pulse- The pain is probably due to ischemia of the chronic. Pain, paresthesia and paresis or nerves and accumulation of metabolites like paralysis is due to ischemia of the peripheral substance P and others of anaerobic metabolism.
Clin Neuropsychol 23:1299– ration of rooflessness in entrants to a hostel for homeless 1314 discount azathioprine 50mg mastercard muscle relaxant allergy, 2009 men buy azathioprine 50 mg mastercard muscle relaxant with painkiller. J Head Trauma ical and cognitive injuries purchase azathioprine paypal muscle relaxant gi tract, their consequences, and services Rehabil 2009, Dec 29 [Epub ahead of print] to assist recovery. J Head Trauma Rehabil Mild Traumatic Brain Injury in the United States: Steps to 8:48–59, 1993 Prevent a Serious Public Health Problem. American Academy of Neurology: Practice parameter: the man- Available at: http://www. Arch Phys Med Rehabil 76:302– American Psychiatric Association: Diagnostic and Statistical 309, 1995 Manual of Mental Disorders, 4th Edition, Text Revision. Armed Forces Health Surveillance Center: New surveillance case Department of Defense: Traumatic brain injury numbers. Armed Forces Health Surveillance Center: Deriving case counts Department of Veterans Affairs, Department of Defense. Med Surveill Mon liability and validity of the Traumatic Brain Injury Question- Rep 17:21, 2010 naire. Brain Inj 19:85–91, Coma Scale–Extended in symptom prediction following 2005 mild traumatic brain injury. Child Abuse Negl 28:1099–1111, 2004 study of inflicted traumatic brain injury in young children. J Head Trauma Rehabil 5:9– Disease Control and Prevention, National Center for Injury 20, 1990 Prevention and Control, 2010. New York, Ox- related hospital discharges: results from a 14-state surveil- ford University Press, 2006 lance system, 1997. Crit Care Nurs Q 23:52–58, 2001 impact of traumatic brain injury: a brief overview. Operation Enduring Freedom 8: Afghanistan, chartered by Consequences of Traumatic Brain Injury. J Head tent postconcussive symptoms and posttraumatic stress dis- Trauma Rehabil 14:602– 615, 1999 order. J Head Trauma Rehabil 23:123– ing of acute mild traumatic brain injury in adolescents. J Head Geneva, World Health Organization, 1992 Trauma Rehabil 25:1–6, 2010 Wu A, Molteni R, Ying Z, et al: A saturated-fat diet aggravates the Winqvist S, Luukinen H, Jokelainen J, et al: Recurrent traumatic outcome of traumatic brain injury on hippocampal plasticity brain injury is predicted by the index injury occurring under and cognitive function by reducing brain-derived neu- the influence of alcohol. Pathological data have been Impact injuries require the head to make contact with an developed through observations of human autopsies and object, with the forces being transmitted to the brain. These biomechanical findings account for the asso- polypathology of human brain injury; and there are likely ciation between subdural hemorrhage and falls or assaults, to be significant differences in the anatomical basis of in- both being situations in which there is a rapid acceleration jury and cellular responses between species. Inertial forces do not require contact, but rather the brain moves within the cranial cavity. Blast injuries are the clinical, pathological, and cellular/molecular features the least well described and are seen in military or terrorist of this complex process. In 2007 a workshop convened by situations; the shock waves from an explosive device can the National Institute of Neurological Disorders and result in injuries to the brain parenchyma. Mechanisms of traumatic brain injury atomical, describing injuries as focal or diffuse, or patho- physiological, based on primary and secondary injuries. Acute cortical contusions involving the In this case the penetrating injury was a metal rod that entered the inferior frontal lobes. On the right side, there is more extensive tissue damage resulting in a laceration (white arrow). There is no direct corre- Focal Diffuse lation with the presence or absence of a skull fracture and Scalp lacerations Global ischemic injury underlying parenchymal brain injury, unless the fracture Skull fractures Traumatic axonal injury/diffuse is depressed and makes direct contact with the underlying vascular injury tissue. However, as discussed later in this chapter, there is Contusions/lacerations Brain swelling a correlation between skull fractures and intracranial hem- orrhages. Intracranial hemorrhage Skull fractures include linear, depressed, and hinge Focal lesions secondary to fractures. In children, growing fractures may be seen raised intracranial pressure where soft tissue becomes trapped between the edges of the fracture, preventing healing. Pathology Associated With Contusions and Lacerations Fatal Head Injury In simple terms, contusions represent bruising of the sur- face of the brain (Figure 2–2). By definition the pia mater is intact overlying contusions but torn in lacerations. They Blunt Force Head Injury: typically involve the frontal poles, the inferior frontal lobe including the gyrus rectus, and medial and lateral orbital Focal and Diffuse Injuries gyri; the temporal poles and lateral and inferior aspects of the temporal lobes; and the cortex above and below the Scalp and Skull Lesions Sylvian fissure. Fractures and contusions may be seen at The scalp and skull may be injured by contact injury. Con- presence of scalp bruising is indicative of contact injury tusions typically involve the crests of gyri and are often su- and in some situations may provide clues to the possible perficial, involving the gray matter only. Occipital bruising is typically asso- may extend into underlying white matter and form a he- ciated with a backward fall and contrecoup contusions in- matoma. In severe cases extensive laceration injury with volving the frontal and temporal tips. Incised wounds are underlying parenchymal hemorrhage may be associated usually insignificant and easily managed in the emergency with subdural hemorrhage, forming a so-called burst lobe. The incidence of skull fractures is associated with the The pattern of contusions may be coup, following a fall severity of the head injury. In coup contusions scalp bruising is over head injury; in clinical practice skull fractures have been the forehead, with the contusions involving frontal and recorded with an incidence of 3% in mild head injury pre- temporal lobes. In contrecoup contusions the same pattern senting to the emergency room, rising to 65% in those re- of contusional injury is associated with bruising in the oc- Neuropathology 25 cipital scalp. Contusions involving the occipital lobes and cerebellum are rare due to the smooth inner surface of the posterior fossa of the skull (compared with the bony ridges of the anterior and middle fossae); when seen they are usu- ally associated with an adjacent skull fracture. This delayed traumatic intracerebral hemor- rhage usually becomes apparent within 48 hours after the head injury. The precise mechanism of this delayed injury is uncertain but is thought to reflect increased blood flow or pressure through a vascular capillary network that is fo- cally damaged, compounded possibly by posttraumatic coagulopathy. At autopsy, in the acute phase contusions are hemor- rhagic and often associated with focal swelling. In time the contusions shrink and take on a golden brown color sec- ondary to hemosiderin deposition (Figure 2–3). Old cortical contusions involving the tusions are a not infrequent incidental autopsy finding, inferior aspect of the frontal lobes. This assesses the extent (score range, 0–3) and depth (score range, 0–4) of contusions in a variety of anatomical locators, producing a numerical score for each hemisphere which is then combined and interpreted as absent, mild, moderate, or severe. The anatomical locators are the fron- tal, temporal, parietal, and occipital lobes; the cortex above and below the Sylvian fissure; and the cerebellum.
Adaptive immunity uses three important features in its method of attack: specificity buy azathioprine line muscle relaxant in pediatrics, diversity azathioprine 50mg low cost muscle relaxant suppository, and memory buy discount azathioprine 50mg on-line spasms vulva. Microbes that escape the onslaught of cells and molecules of the innate immune system face attack by T cells, B cells, and B-cell products of the adaptive immune system, also called the acquired immune system. The adaptive immune system: Is a relatively recent evolutionary development and characteristic of jawed vertebrates Is activated by thousands of diverse antigens, which are presented as glycoproteins on the surface of bacteria, as coat proteins of viruses, as microbial toxins, or as membranes of infected cells Responds with the proliferation of cells and the generation of antibodies that specifically assault the invading pathogens Responds slowly, being fully activated about 4 days after the immunologic threat Is capable of immunologic memory, so that repeated exposure to the same infectious agent results in improved resistance against it Specificity The specificity of the adaptive immune system is created by antigen recognition molecules, which are synthesized prior to the exposure to antigen and, in B lymphocytes, can be modified during the immune response to make them even more specific to the antigen. Each class of antibody plays a unique role in immune defense and will be discussed later in the chapter. To stay with the example of antibodies, most protein antigens have several epitopes (the part of the antigen that binds the antibody) and, hence, are recognized by different B cells, which release different antibodies to mount a polyclonal antibody response. On the other hand, closely related antigens may share epitopes (cross-reactivity). Diversity The diversity of adaptive immune responses is based on a huge variety of antigen receptor configurations, essentially one receptor for each different antigen that might be encountered. The molecule diversity is mainly achieved by variable recombination of gene segments prior to exposure to antigen and, in the case of immunoglobulins, additionally by mutation of the molecules after exposure to antigen. The recognition of an antigen by the lymphocyte with the best-fitting receptor occurs mainly in the local lymph node and induces the activation, proliferation, and differentiation of the responsive cell, a process known as clonal selection. Only the clone of the lymphocyte that has the unique ability to recognize the antigen of interest proliferates and generates progenitor cells. These cells are specific to the inducing antigen but may have different functions. In the case of B cells, plasma cell clones produce antibodies, and memory cell clones enhance subsequent immune responses to the specific antigen. Clonal selection amplifies the number of T or B lymphocytes that are programmed to specifically respond to the inciting stimulus. Plasma cells are much larger and are capable of producing and secreting antibodies. Initially, the plasma cells produce IgM antibodies and later can switch to produce IgG, IgA, or IgE antibodies when antibodies with different functional capabilities are needed. Similarly, clonal proliferation of T cells can lead to the generation of more antigen-specific T cells and to the production of effector T cells, such as T helper and cytotoxic T cells, and memory T cells. Memory The memory of the adaptive immune system is based on the fact that some descendants in the expanded B- cell and T-cell clones function as memory cells (see Fig. These cells mimic the reactive specificity of the original lymphocytes that responded to the antigen and accelerate the responsiveness of the immune system when the antigen is encountered again (anamnestic response) and are the basis for immunization via vaccinations. As mentioned previously, though presented as distinct systems, no part of the immune system works separately. Rather, they all work in a cooperative fashion using cytokines and other means as a communication system. B cells mediate the humoral immune response, whereas T cells regulate the cell-mediated immune response. These cells form, with each other and with other immune cells, a complex network of communication and immune response that is the basis for the efficiency, flexibility, and longevity of the adaptive immune system. The figure is organized according to the type of encountered antigen (exogenous or endogenous, left), to the sensing and responding processes (antigen recognition and presentation and immune response, top), and to the involvement of T cells and B cells (cellular and humoral immune responses, right). Activated T cells accomplish cellular immune responses, and B cells and antibodies mediate humoral immune responses. The immune response involves two paths, one using B cells (humoral immune response) and one using cytotoxic T cells (cellular immune response). Millions of different B and T cell types exist to recognize millions of different antigens. Dendritic cells are mostly found in peripheral tissue, where they ingest, accumulate, and process antigens. Hence, they present the particular antigen to which the antibody that they express is directed. Similarly, exposure to foreign antigen from a tissue graft triggers an immune reaction in the body. This occurs when the tissues of the donor and the recipient are not histocompatible, which explains the origin for the name “major histocompatibility complex. There are more than 160 known clusters that coat the surface of leukocytes and many other cells. This is a critical step because during this time they develop their ability to distinguish self from nonself peptides. After positive selection, cells undergo negative selection in the medulla of the thymus. This is important because these cells would have later reacted with self-peptides and caused autoimmune diseases. Killer, helper, and memory T cells Killer T cells, helper T cells, and memory T cells can be distinguished based on their immunologic + function. These cells have no cytotoxic activity and do not directly kill infected cells or clear pathogens. Instead, helper T cells control the immune response by directing other cells to perform these tasks. They stimulate proliferation of B cells and cytotoxic T cells, + attract neutrophils, and activate macrophages. The resultant actions, called T helper 1 response, or type 1 response, support activities of macrophages and cytotoxic T cells of the cellular immune system. On the other hand, T helper 2 cells produce effector molecules, such as interleukin-4, interleukin-5, interleukin-13, interleukin-25, interleukin-31, and interleukin-33, among numerous other cytokines. This T helper 2 response, or type 2 response, promotes the actions of B cells and hence the humoral immune system. Additionally, other immune cells express many of the specific T-cell cytokines as well. Several new models have been proposed that include T helper 17 cells, but as of today, there is no unanimously accepted approach. All have in common the ability to suppress immune responses and, hence, are important in maintaining immune homeostasis. For instance, they are known to inhibit the production of cytotoxic T cells when they are no longer needed. On the other hand, it has been shown that T helper cells are also capable of “regulating” their own responses. Regulatory T cells are thought to be associated with induction of tolerance to microbiota at mucosal surfaces. Lastly, memory T cells are lymphocytes that become “experienced” by having encountered an antigen during a prior infection or a previous vaccination, or a cancer cell. Memory T cells, when encountering an invader (pathogen) for the second time, mount a faster and stronger immune response than they did the first time. T helper cells are absolutely required for B-cell memory cells to develop and antibody class-switching events to occur. Time delay in cell-mediated immunity T cells and their products may exert their effects in concert with other effector cells, such as neutrophils, eosinophils, and mast cells. The secretion of T-cell factors that recruit and activate other cells takes time, and thus, the consequences of T-cell activation are not noticeable until 24 to 48 hours after antigen challenge.
By H. Delazar. Brewton-Parker College.