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Mice infected with African trypanosomes produce exceptionally large amounts of serum IgM, a
major part of which binds to non-trypanosome antigens such as trinitrophenol and single-strand
DNA. In this paper, we describe that in cattle infected with Trypanosoma congolense and T. vivax,
similar antibodies are found, although they bind mainly to protein antigens, such as b-galactosidase,
ovalbumin and ferritin. The parasite non-specific IgM antibodies appear around the same time as
the parasite-specific antibodies, but their origin and function are not clear.We tested the hypothesis
that CD5+ B cells (or B-1 cells), which increase during trypanosome infections in cattle, are
responsible for production of antibodies to non-trypanosome antigens. Splenic CD5+ and CD5−
B cells from infected cattle were sorted and tested in a single cell blot assay. The numbers of
immunoglobulin-secreting cells were similar in both B-cell populations. However, antibodies with
reactivity for non-trypanosome antigens were significantly more prevalent in the 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 antibodies. We propose that these
antibodies are natural, polyreactive antibodies that are predominantly secreted by CD5+ B cells.
Since B-1 cells are up-regulated in many states of immune insufficiency, the immunosuppression
associated with trypanosome infections may be responsible for the increase of this subset and the
concomitant increase in trypanosome non-specific antibodies. |
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