Immunology Flashcards
Why do IgG antibodies against hepatitis C envelope proteins not provide immunity against infection?
The envelope proteins have variations in their antigenic structure due to an RNA-dependent RNA polymerase with no proofreading 3’→5’ exonuclease activity (error prone).
What are common features of sarcoidosis?
African American younger adults. Cough and dyspnea. Skin lesions, uveitis, Lofgren syndrome. Imaging shows bilateral hilar adenopathy. Elevated angiontensin converting enzyme and hypercalcemia/hypercalciuria (granulomas produce and secrete ACE and vitamin D). Noncaseating granulomas seen on pathology. CD4+ T cells predominate with a high CD4+/CD8+ ratio in bronchoalveolar lavage fluid.
What is etanercept?
It is a tumor necrosis factor-alpha inhibitor. It is added to methotrexate to treat moderate-to-severe rheumatoid arthritis in patients who have failed MTX therapy alone. It is a fusion protein linking a soluble TNF-alpha receptor to the Fc component of human IgG. It reduces the activity of TNF-alpha by acting as a decoy receptor. The suffix “-cept” represents a receptor molecule.
How do eosinophils play a role in host defense against parasitic infections?
When stimulated by antibodies bound to parasitic organisms, they destroy the parasites via antibody-dependent cell-mediated cytotoxicity (ADCC). This involves degranulation and release of cytotoxic proteins (e.g. major basic protein) and reactive oxygen intermediates. Macrophages, neutrophils and NK cells also use ADCC.
Eosinophils also are involved in late-phase type 1 hypersensitivity reactions and chronic allergic reactions (not helpful for fighting parasites).
What is Chédiak-Higashi syndrome?
Autosomal recessive syndrome consisting of immunodeficiency (get recurrent pyogenic infections by strep and staph), albinism, and neurologic defects (e.g. nystagmus, peripheral and cranial neuropathies). Causes by a defect in lysosomal trafficking regulator gene (LYST). This causes microtubule dysfunction in phagosome-lysosome fusion. Also, neutrophils, CD8+ cells and melanocytes fail to release granules.
What cell type is responsible for the intense inflammatory response seen in gout?
Neutrophils
What is systemic mastocytosis?
Clonal mast cell proliferation due to KIT receptor tyrosine kinase mutations. This causes excessive histamine release due to degranulation of mast cells. Symptoms include syncope, flushing, hypotension, pruritis, urticaria, and abdominal cramps. It may also cause gastric ulceration due to increase acid production.
What are features of leukocyte adhesion deficiency (LAD)?
Due to an absence of CD18 antigens, which are necessary for the formation of integrins (needed for leukocyte adhesion to endothelial surfaces). Patients with LAD get recurrent skin and mucosal infections (often due to Staph aureus or gram-negative rods) and periodontal disease. Infection is notable for lack of purulence due to absence or leukocytes in peripheral tissues. Wound healing is also impaired, including late separation (>21 days) of the umbilical cord. Persistent leukocytosis is a common finding due to leukocytes not being able to migrate out of the blood vessels.
What medications cause medication-induced IgE-independent mast cell activation?
Opioids, radiocontrast agents, and some antibiotics (e.g. vancomycin). They can induce mast cell degranulation by activation of protein kinase A and PI3 kinase. This results in release of several mediators, including histamine, bradykinin, heparin, and a number of enzymes and chemotactic factors. Common symptoms include diffuse itching and pain, bronchospasm, and localized swelling.
Do not confuse with IgE-mediated degranulation, which can be causes by environmental exposures (e.g. food, stings) and certain medications (e.g. beta-lactam and sulfonamide antibiotics).
What are Langhans giant cells?
They are large cells found in granulomatous conditions, such as tuberculosis. They are formed by the fusion of macrophages, and contain nuclei arranged in a horseshoe-shaped pattern in the cell periphery
What cytokine is responsible for B-cell antibody class switching?
IL-4. It is secreted by Th2 lymphocytes along with IL-5. Both IL-4 and IL-5 help to activate B-cells, by IL-4 is primarily responsible for signaling B-cells to class switch from IgM to IgG, IgA or IgE. IL-4 is also responsible for stimulating differentiation of Th0 (naïve) T-cells into Th2 helpers.
What is tryptase?
It is released from mast cells in response to allergic reactions, such as anaphylaxis. Tryptase is relatively specific to mast cells, and elevated serum levels of tryptase are often used to support a clinical diagnosis of anaphylaxis after a patient has been stabilized.
What HLA allele is associated with reactive arthritis following GU infections by Chlamydia trachomatis or bacterial enteritis (e.g. Salmonella, Shigella, Yersinia, Campylobacter, or C. diff)?
HLA-B27
What is the mechanism behind sarcoidosis?
Cell-mediated immune response driven by TH1 type CD4+ helper T cells, which secrete IL-2 and interferon-𝛾. IL-2 stimulates autocrine proliferation of TH1 cells. INF-𝛾 activates macrophages, promoting granuloma formation.
What tumor is common in myathenia gravis?
Thymoma
