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Table 9.1 Functional aspects of T and B cells. T cells B cells Origin Thymus Bone marrow Tissue distribution Parafollicular areas of cortex in nodes, periarteriolar in spleen Germinal centres of lymph nodes, spleen, gut, respiratory tract; also subcapsular and medullary cords of lymph nodes Blood 80% of lymphocytes; CD4 > CD8 20% of lymphocytes Membrane receptor TCR for antigen BCR (= immunoglobulin) for antigen Function CD8+: CMI against intracellular organisms CD4+: T-cell help for antibody production and generation of CMI Humoral immunity by generation of antibodies Characteristic surface markers CD1 CD2 CD3 CD4 or 8 CD5 CD6 CD7 HLA class I HLA class II when activated CD19 CD20 CD22 CD9 (pre B cells) CD10 (precursor B cells) CD79 a and b HLA class I and II Genes rearranged TCR α, β, γ, δ IgH, Igκ, Igλ BCR, B-cell receptor; C, complement; CMI, cell-mediated immunity; HLA, human leucocyte antigen; Ig, immunoglobulin; TCR, T-cell receptor. Table 9.2 Some properties of the three main classes of immunoglobulin (Ig). IgG IgA IgM Molecular weight 140 000 140 000 900 000 Normal serum level (g/L) 6.0–16.0 1.5–4.5 0.5–1.5 Present in Serum and extracellular fluid Serum and other body fluids (e.g. of bronchi and gut) Serum only Complement fixation Usual Yes (alternative pathway) Usual and very efficient Placental transfer Yes No No Heavy chain (γ1–4) α (α1 or α2) μ Untitled-5.indd 21 2/8/2011 11:48:05 AM Table 9.3 Causes of lymphocytosis. Infections Acute: infectious mononucleosis, rubella, pertussis, mumps, acute infectious lymphocytosis, infectious hepatitis, cytomegalovirus, HIV, herpes simplex or zoster Chronic: tuberculosis, toxoplasmosis, brucellosis, syphilis Chronic lymphoid leukaemias (see Chapter 17) Acute lymphoblastic leukaemia Non-Hodgkin lymphoma (some) Thyrotoxicosis HIV, human immunodeficiency virus. Table 9.4 Classification of immunodeficiencies. Primary B cell (antibody deficiency) T cell Mixed B and T cell Secondary B cell (antibody deficiency) T cell T and B cell X-linked agammaglobulinaemia, acquired common variable hypogammaglobulinaemia, selective IgA or IgG subclass deficiencies Thymic aplasia (DiGeorge’s syndrome), PNP deficiency Severe combined immune deficiency (as a result of ADA deficiency or other causes); Bloom’s syndrome; ataxia-telangiectasia; Wiskott– Aldrich syndrome Myeloma; nephrotic syndrome, protein-losing enteropathy, anti-CD20 (rituximab) therapy AIDS; Hodgkin lymphoma, non-Hodgkin lymphoma; drugs: steroids, ciclosporin, azathioprine, fludarabine, etc. Chronic lymphocytic leukaemia, post-stem cell transplantation, chemotherapy/radiotherapy, anti-CD52 (alemtuzumab) ADA, adenosine deaminase; AIDS, acquired immune deficiency syndrome; Ig, immunoglobulin; PNP, purine nucleoside phosphorylase. Untitled-5.indd 22 2/8/2011 11:48:05 AM