CD5(-LYMPHOCYTES ARE THE MAIN SOURCE OF ANTIBODIES REACTIVE WITH NON-PARASITE ANTIGENS IN TRYPANOSOMA CONGOLENSE-INFECTED CATTLE() B)

Mice infected with African trypanosomes produce exceptionally large am ounts of serum IgM, a major part of which binds to non-trypanosome ant igens such as trinitrophenol and single-strand DNA. In this paper, we describe that in cattle infected with Trypanosoma congolense and T. vi vax, similar antibodies are found, although they bind mainly to protei n antigens, such as beta-galactosidase, ovalbumin and ferritin. The pa rasite non-specific IgM antibodies appear around the same time as the parasite-specific antibodies, but their origin and function are not cl ear. We tested the hypothesis that CD5(+) B cells (or B-1 cells), whic h increase during trypanosome infections in cattle, are responsible fo r production of antibodies to non-trypanosome antigens. Splenic CD5(+) and CD5(-) cells from infected cattle were sorted and tested in a sin gle cell blot assay. The numbers of immunoglobulin-secreting cells wer e similar in both B-cell populations. However antibodies with reactivi ty for non-trypanosome antigens were significantly more prevalent in t he CD5(+) B-cell fraction and were exclusively IgM. The preference for production of these antibodies by CD5(+) B cells and the expansion of this subpopulation during infections in cattle, strongly suggest that CD5(+) B cells are the main source of trypanosome non-specific antibo dies. We propose that these antibodies are natural, polyreactive antib odies that are predominantly secreted by CD5(+) B cells. Since B-1 cel ls are up-regulated in many states of immune insufficiency, the immuno suppression associated with trypanosome infections may be responsible for the increase of this subset and the concomitant increase in trypan osome non-specific antibodies.