Unsuspected varicella-zoster virus encephalitis in a child with acquired immunodeficiency syndrome

Novel techniques have made possible in situ analyses of the lymphocyte populations responding to antigen. In the spleen, antigen-specific T and B cells are first observed in the periarteriolar lymphoid sheath. Following conjugate formation between specific T and B lymphocytes, B-cell proliferation and differentiation takes place in two distinct sites, the periarteriolar lymphoid sheath-associated foci and germinal centers.