Differential secretion of interleukin-12 (IL-12) subunits and heterodimeric IL-12p70 protein by CD-1 mice and murine macrophages in response to intracellular infection by Brucella abortus

The secretion of interleukin-12 (IL-12) following intracellular infection w ith virulent Brucella abortus strain 2308 was investigated in CD-1 mice and in CD-1 cultured peritoneal macrophages, Bioactive IL-12p70 and free non-i mmunoactive p40 subunits (IL-12p40) were determined by enzyme-linked immuno sorbent assays. In CD-1 mice, B. abortus 2308 was a potent inducer of IL-12 p40 (maximum levels mere 5.9 and 3.4 ng/ml in sera and spleen homogenates, respectively). Secretion of IL-12p70 was also demonstrated in vivo, althoug h at much lower levels (216.6 and 198.9 pg/ml in sera and spleen homogenate s, respectively). Production of IL-12 over the first 7 days after infection was accompanied by active multiplication of B. abortus in the spleens of i nfected mice. CD-1 cultured peritoneal macrophages secreted only IL-12p40 ( 878.4 pg/10(7) macrophages) in response to B. abortus infection and no prod uction of IL-12p70 was observed. In contrast, CD-1 peritoneal macrophages s ecreted detectable amounts of IL-12p70 (16.2 pg/10(7) macrophages) in respo nse to purified lipopolysaccharide (S-LPS) from B, abortus 2308. The macrop hages also secreted significant amounts of interferon-gamma (IFN-gamma) (52 0.1 pg/10(7) macrophages) in response to intracellular B. abortus, These re sults indicate that B. abortus 2308 is not a potent inducer of IL-12p70 pro duction, whereas purified S-LPS from B. abortus 2308 induces the secretion of this bioactive form of IL-12 in cultured peritoneal macrophages. CD-1 pe ritoneal macrophages were able to secrete IFN-gamma, as well as high amount s of IL-12p40, in response to intracellular infection by B. abortus.