Brain tumor-infiltrating plasma cells or circulating antibody account for endogenous reactivity to secondary antibody

AbstractMechanisms of immune response associated with immunotherapy remain controversial, and the role of the antibody response in the efficacy of immunotherapy has largely been ignored. By the use of immunohistochemistry to search for the presence of antibodies and antibody-secreting plasma cells, the role of antibody response immunotherapy was examined. By the use of an antimouse immunoglobulin antibody reactive against all isotypes, cells consistent with plasma cell morphology and immunophenotype were observed more frequently in the tumor (but not normal brain) of vaccinated mice. Additionally, high levels of what appeared to be nonspecific and diffuse localization of secondary antibody also were observed. This staining is absent, however, in B/plasmacell-deficient mice, suggesting that secreted antibodies are present in the tumors of wild-type mice. Animals deficient for B/plasma cells did not respond to immunotherapy when compared with vaccinated wild-type animals. Thus, the use of immunohistochemist...