Walsh & Hoyt: Immunity and Infectious Disease

The increasing recognition of the role of cellular and humoral reactions in disease has led to a greater understanding of the pathogenesis of infection of the CNS. Depending on the immune response, the same organism may produce no, mild, recurrent, or fatal disease. The CNS is at a disadvantage when it comes to admitting or producing antibodies because serum proteins are unable to diffuse easily into it. Immunoglobulin G (IgG) and IgA normally are present in the cerebrospinal fluid (CSF), but IgM is not, presumably because of its greater molecular weight. Complexes of antigens and antibodies are likely to be formed whenever there is an immune response of a humoral type. Such complexes also may form within blood vessels, producing a vasculitis, or within neural tissue itself.