Allogeneic reactivity in normal mouse serum.

Normal C57BL/6 (B6) mouse serum was tested in the direct cytotoxicity assay for specific reactivity against lipopolysaccharide (LPS)-stimulated mouse spleen cells. Selective reactivity was found in weanling and adult serum against lymphoblasts from mice that express an antigen encoded by the H-2Kk region of the major histocompatibility complex (MHC). Other strains, congenic with B6 at the MHC, did not exhibit the same alloreactivity. Serum from mice of a congenic strain being derived in our laboratory, which differs from B6 at two unlinked loci, Tla and nu, exhibited similar reactivity against the B6-H-2k LPS-stimulated lymphoblasts, implying that a competent T cell compartment is not necessary for generation of this reactivity. Such reactivities may result from environmental stimulation of the immune system, from internal immunoregulatory controls, or from some combination of these immune stimuli.