a surface antigen on *helper T cells that is particularly important for immune resistance to viruses. It is also a receptor for the human immunodeficiency virus (HIV); progressive reduction of CD4-bearing T cells reflects the progression of *AIDS.
an inherited immunodeficiency syndrome characterized by normal or high IgM levels with absence of IgA, IgG, and IgE (see immunoglobulin). Patients are susceptible to bacterial and opportunistic infections. Some cases are due to a mutation in the gene encoding the CD40 ligand, which is synthesized by *helper T cells and is involved in activation of B cells to produce circulating antibodies.... hyper-igm syndrome
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