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Saturday, December 25, 2010
lymphoid organs (Organs of the Immune System)
The organs of the immune system are positioned throughout the body. They are called lymphoid organs because they are home to lymphocytes, small white blood cells that are the key players in the immune system.
Bone marrow, the soft tissue in the hollow center of bones, is the ultimate source of all blood cells, including ......................
A neutrophil travels along the capillary endothelial layer. Endothelial cells are triggered to express selectins on their surface for neutrophil integrin-mediated adherence. Transendothelial migration allows the neutrophil to traverse the blood endothelial layer. Squeezing into the extra-capillary space where migration towards a chemotactic gradient (chemotaxis) helps it to locate the pathogen. Subsequent phagocytosis ensues.
These are a focus of central fibrinoid necrosis surrounded by a palisade of epitheloid cells, occurring as a typical feature of sero-positive rheumatoid arthritis..............
A 77-year-old woman underwent surgical resection of a 1.5-cm papillary carcinoma of the right breast. Isosulfan blue dye (8 ml) was used intraoperatively to define the associated lymphatic drainage.
Three sentinel nodes were excised from her axilla 5 minutes later, followed by the lumpectomy. By the time of wound closure, blue hives had developed on both upper arms and the chest as a result of an allergic reaction to the dye. Her cardiorespiratory system remained stable.
She was treated with intravenous phenylephrine (50 mg), had an uneventful recovery, and was discharged home 4 hours later. Blue hives occur in up to 1.5% of patients injected with this dye; the cause is probably a type I, IgE-mediated hypersensitivity to the dye.
A patient has secondary antibody deficiency due to B-cell suppression His primary pathology is likely to be
a) Waldenstrom macroglobulinemia b) X-linked agammaglobulinemia c) immunoglobulin A deficiency d) immunoglobulin M deficiency e) common variable immunodeficiency
The correct answer is A
Explanation Antibody immunodeficiency can be primary or secondary. Secondary antibody deficiency due to B-cell suppression can occur with multiple myeloma, Waldenstrom macroglobulinemia, or chronic lymphocytic leukemia. Secondary deficiencies leave patients susceptible to the same pathogens that can cause recurrent pneumonia in patients with primary antibody deficiencies Primary antibody deficiencies include X-linked agammaglobulinemia, common variable immunodeficiency, selective immunoglobulin A or immunoglobulin M deficiency, and hyperimmunoglobulin M immunodeficiency. These disorders are characterized by chronic or recurrent pyogenic infection, especially pneumonia, caused by encapsulated bacteria (eg, S pneumoniae, H influenzae, and S aureus) and P aeruginosa . Untreated or recurrent pneumonia may lead to bronchiectasis.
The main cell of the specific immune response is the small lymphocyte.
LIMPHOCYT RECIRCULATION 1) B and T lymphocytes constantly enter the blood stream from the peripheral lymphatic tissue via the lymphatics and the thoracic duct and circulate around the body. '
2) They reenter the lymphoid tissue at another site.
3) Lymphocytes form 20 - 40% of the circulating white blood cell Circulating lymphocytes are mainly T cells with a few B cells.
Immune response & elimination of antigen 1) Antigens can enter the body through the mucosa or skin.
2) Meeting the mucosa associated lymphoid tissue or the cutaneous lymphoid tissue.
3) The antigens are carried to the regional lymph nodes via lymphatics
4) If the antigen enters the blood stream it will be filtered by the spleen.
5) Lymphocyte recirculation ensures that B and T lymphocytes are constantly patrolling the body looking for antigen.
6) Antigen will meet the corresponding lymphocytes specific for the antigen →immune response (activation, proliferation and differentiation of lymphocytes)
7) The immune response takes place in the PERIPHERAL LYMPHOID TISSUE(rich in macrophages and dendritic cells).
* At the mucosal or skin surface immune response takes place in the MALT or cutaneous immune system.
* o The immune response to tissue antigens takes place in the lymph node.
* o The immune response to circulating antigens takes place in the spleen.
8) Antibodies from B cells or effector T cells go to the site of infection and eliminate the antigen.
9) The memory cells remain in the lymphoid tissue.
10) The second time the antigen enters there are a large number of antigen specific lymphocytes (memory cells) in the lymphoid organs so the secondary response is faster and greater than the primary response.
CYTOKINES
1) Cytokines are small soluble proteins that act as multipurpose chemical messengers,secreted by a cell, and act on itself or another cell to change the activity of that cell.
2) They play an important role in both non-specific and specific immunity.
3) cytokines Can be produced by a wide variety of cells such as endothelial cells etc.
4) Some cytokines act on the bone marrow to increase cell proliferation and differentiation.
* eg. colony stimulating factors include GM-CSF, G-CSF, M-CSF.
Feature of cytokines
1) ONE cytokine can ACT on many different cells.
* e.g. TNF acts on the liver to produce acute phase proteins and on the Neutrophils to activate it.
2) DIFFERENT cytokines can have the SAME action.
* e.g. TNF from macrophages and lymphotoxin from T cells have the same actions.
3) Cytokines can act on the same cell that produced it (AUTOCRINE ACTION), on nearby cells (PARACRINE ACTION) or on distant cells (ENDOCRINE ACTION).
with a HIV positive person or if the person is a HIV risk group (gay or bisexual men, injection drug users or sex workers), and if the exposure is isolated and the patient is commited to safer sex in the future and the exposure occurred within 72 hours of presentation for care.
Exposure to persons known to be HIV infected
if medication regimen of source patient is unknown => prescribe Zivudine (AZT/ZDV) 300mg bid + Lamivudine (Epivir) 150mg bid + Indinavir (Crixivan) 800mh q8h or nelfinavir (Virasept) 1250mg bid or 750mg tid
Combivir 1 tablet bid may be substituted for zidovudine and lamivudine
if medication regimen of source patient is known => prescribe 2 NRTIs and 1 protease inhibitor that are different from the source patient's regimen
possible substitues for zidovudine and lamivudine:- stavudine (d4T/Zerit) 40mg bid for > 60kg and 30mg bid <> 60kg and 125mg for <>
Exposure to person or persons of unknown HIV status but who probably have high HIV risk factors :
significant exposures => treat as if an exposure to a known HIV-infected person with an unknown medication regimen, as above
exposures that might result in HIV infection => treat with zidovudine and lamivudine without a protease inhibitor
Exposure to person or persons of unknown HIV status but who probably have low HIV risk factors
significant exposures => treat with zidovudine and lamivudine. A protease inhibitor could be added if the patient requests it, if the provider believes that the exposure history is unclear, other exposures also occurred, or if other factors relating to exposure history or HIV status are compelling
exposures that might result in HIV infection => treat with zidovudine and lamivudine without a protease inhibitor
Additional caveats
* PEP should not be provided to patients whose exposure history has no known possibility for HIV transmission
* PEP should not be given to persons already infected with HIV
* providers may consider PEP for any patient who appears to be at risk after an HIV exposure but whose circumstances are not delineated in the above categories
Providers are reminded that PEP should only be prescribed as part of a comprehensive program to reduce future HIV risk-related behaviours. Multiple prescription requests for PEP should be strongly discouraged and must be averted through risk reduction counselling.
Definitions: High HIV risk factors: trading sex for drugs or money, IV drug use, unprotected anal or vaginal intercourse with persons with HIV risk factors
Significant exposures include the following: anal or vaginal intercourse without a condom or with condom breakage; exposure to semen or blood onto mucosal or nonintact surfaces, and intravenous needle sharing
Examples of exposures that might result in HIV infection are as follows: cunnilingus, fellatio, semen or blood on healing skin wounds
Bone marrow, the soft tissue in the hollow center of bones, is the ultimate source of all blood cells, including ......................
