[Primary immune deficiencies of B-lymphocytes]

Primary B-cell immunodeficiency is relatively frequent and may result in recurrent bacterial infections involving notably the respiratory tract, and in chronic severe enteroviral infections in patients with agammaglobulinaemia. Selective IgG2 isotype deficiency results in pneumococcal, Haemophilus influenzae and pseudomonal infections, since it is associated with defective production of antibodies that are specifically directed against bacterial capsular polysaccharides. Progress has recently been achieved in the determination of genetic and molecular bases of some of these immunodeficiencies. In X-linked agammaglobulinaemia, the abnormal gene has been located on the long arm of the X chromosome (Xq22-23); the intrinsic B-cell abnormality blocks differentiation at the pre-B stage, before the genes coding for light chain immunoglobulins are rearranged. There is now a strong suspicion that IgA deficiency, hypoglobulinaemia with variable expression and some selective IgG isotype deficiencies are three ways of expressing one single abnormality a genetic factor of which is located in the class III region of the HLA complex and perhaps also associated with HLA class II DQ. Treatment of deficient IgG production with intravenous immunoglobulin has thoroughly altered the prognosis of these diseases. Complete IgA deficiency carries a risk of accident by production of anti-IgA antibodies, which means that patients with isolated IgA deficiency should not be treated, that these antibodies should systematically be looked for in patients with IgA deficiency associated with partial deficiency of other immunoglobulins, and that these patients should be treated with IgA-free immunoglobulin preparations.