INTERLEUKIN-12 IS PRODUCED IN-VIVO DURING ENDOTOXEMIA AND STIMULATES SYNTHESIS OF GAMMA-INTERFERON

Gamma interferon (IFN-gamma) is produced in response to circulating li popolysaccharide (LPS) and contributes to the lethality of endotoxic s hock. To address the cellular source of IFN-gamma production in vivo, T cells and B cells were magnetically purified from C57BL/6 mouse sple ens 5 h following endotoxin injection. IFN-gamma RNA was abundant in s plenic CD4(+) and CD8(+) T cells and in a T- and B-cell-depleted popul ation of splenocytes containing 34% NK1.1(+) natural killer (NK) cells . Because interleukin 12 (IL-12) is a known inducer of IFN-gamma synth esis by cultured T cells and NK cells, we examined whether IL-12 might be involved in IFN-gamma release during endotoxemia. mRNA encoding th e p40 subunit of IL-12 increased markedly in the spleens of C57BL/6 mi ce at 2 h after LPS injection, whereas p35 IL-12 mRNA was constitutive ly expressed at ail times. Bioactive IL-12 (p70 heterodimer) was detec ted in mouse serum at 2 to 4 h after LPS injection. Similar results we re obtained using a p40 subunit-specific enzyme-linked immunosorbent a ssay. Endotoxin-insensitive C3H/HeJ mice generated threefold less IL-1 2 p70 and IFN-gamma at these times than endotoxin-sensitive C3H/HeOuJ mice. Pretreatment of mice with polyclonal anti-mouse IL-12 antibody r educed IFN-gamma levels present at 6 h post-LPS nearly sixfold in thre e separate experiments. These studies support a role for IL-12 as a pr oximal stimulator of IFN-gamma release during endotoxemia.