Hypogammaglobulinemia is a disorder that is caused by a lack of B-lymphocytes and a resulting low level of immunoglobulin (antibodies) in the blood. Immunoglobulin plays a dual role in the immune system by recognizing foreign antigens and triggering a biological response that culminates in the elimination of the antigen. Antibody deficiency is associated with recurrent infections with specific types of bacteria. In pure B-cell disorders, cellular immunity generally is intact and the frequency of viral, fungal, and mycobacterial (e.g. tuberculosis) infections is not increased. There are 5 major types of immunoglobulin: immunoglobulin G, immunoglobulin M (IgM), immunoglobulin A (IgA), immunoglobulin D (IgD), and immunoglobulin E (IgE).