Several strains of mutant C57BL/6 mice (TCR-/-, C3-/-, CD16-/-, MyD88-/-, TRIF-/-, INFγ-/-, TNFR1-/-, Gal3-/-, Prf1-/-) with defects in innate and adaptive immunity were examined for expression of this infection-induced, immunosuppressive trait. This evidence concerns the gene C3 and infection.