The role of endogenous interleukin-12 in resistance to murine cytomegalovirus (MCMV) infection and a novel action for endogenous IL-12 p40

Biologically active interleukin-12 (IL-12), comprising a 40 kDa subunit (p40) covalently linked to a 35 kDa subunit (p35), is produced in response to a range of infectious stimuli. Here, me demonstrate that mice deficient in either IL-12 p30 (p40(-/-)) or IL-12 p35 (p35(-/-)) are susceptible to murine cytomegalovirus (MCMV) infection in terms of survival (Balb/c p35(-/-)) and viral clearance (Balb/c p35(-/-) and Balb/c p30-/-), and this susceptibility may be correlated to a deficiency in serum interferon-gamma (IFN-gamma) levels. These data support a role for endogenous IL-12 in controlling MCMV infection. The IL-12 p30 subunit is produced in excess of IL-12 p35, and to date the function of the excess endogenous p40 has been assumed to be one of IL-12 antagonism, as demonstrated by experiments with exogenous p40 both in vivo and in vitro, We show that Balb/c p35(-/-) alone are significantly compromised in survival of a sublethal infection and in clearance of virus from the spleen. These mice produce a very early IFN-gamma spike (8 h after infection) and an aberrant tumor necrosis factor-alpha (TNF-alpha) spike (day 2 after infection). MCR IV infection has revealed an altered Balb/c p35(-/-) phenotype compared with Balb/c p40(-/-), and this indicates that endogenous p30 may have an activity independent of and additional to IL-12 antagonism in vivo.