Cross-reactivity of IgM-secreting B cells from normal BALB/c mice.

Cross-reactive antibodies capable of binding to foreign and self Ag are present in the serum of normal newborn and adult animals. In our work, a chamber ELISA assay was used to quantitate the cross-reactivity of B cells actively secreting Ig in BALB/c mice of different ages. Individual lymphocytes were tested for the production of IgM antibodies capable of binding to a series of four unrelated Ag (DNA, TNP, actin, and OVA). Results indicate that nearly one-quarter of IgM secreting lymphocytes from 6-day-old animals were cross-reactive. This frequency was two- to fourfold higher than that found in adult mice. Very old animals, however, showed a selective increase in the cross-reactivity of anti-DNA (but not anti-TNP) secreting lymphocytes. Evidence from Ag inhibition experiments indicated that low concentrations of soluble Ag could block the binding of polyreactive antibodies, and that approximately one-half of "naturally" cross-reactive B cells produced antibodies capable of binding to three or more unrelated Ag.