. Block in B cell differentiation due to defective interaction between T and B cells. Naive B cells are not able to differentiate into IgA - producing cells. Features --> . Respiratory infections . Chronic diarrheal diseases . Increased incidence of asthma and other atopic disease . Frequent production of autoantibodies . Association with ahritis and SLE . Reduction of IgG2 and IgG4 Treatment - . Symptomatic . No benefit of immunoglobulin (IgA) infusion because of increased risk of development of autoantibodies against IgA. . Exceptionally immunoglobulin infusion may help in patients with IgG2 and IgG4 deficiency. Common variable immunodeficiency . The feature common to all patients is hypogammaglobulinemia generally affecting all the antibody classes but sometimes only IgG. . Pathogenesis ---> . Patients have normal numbers of B cells. . B cells are not able to differentiate into plasma cells. . Features - . Recurrent sinopulmonary infections . Recurrent herpesvirus infection . Persistant diarrhea caused by G lambia . Meningoencephalitis caused by enterovirus. . High incidence of autoimmune diseases eg. R.A. . Increased risk of lymphoid malignancy and gastric cancer, paicularly in women. . Relatives of these patients have high incidence of selective IgA deficiency. . T/t I.V. immunoglobulin Note : AIDS is a type of secondary immunodeficiency (not primary).">