Role of the fourth complement component (C4) in the regulation of contact sensitivity. III. In vivo effect of purified C4.

Lymph node cells obtained from CBA/J mice 4 days after painting with contact sensitizing agents such as picryl chloride or oxazolone ("4-day" cells), induce contact sensitivity into naive recipient mice by membrane-associated immunocomplexes. This immunizing capacity is abolished after incubation of the cells in serum from mice with high C4 levels (C4H), but not in serum from mice with low C4 levels (C4L), and the inhibitory activity of C4H serum is due to the activation of the early components of the classical complement pathway. The presence of 4-day cells depends on C4 levels: in fact, C4H mice lack these cells because they activate their own complement in vivo, whereas C4L mice fail to activate complement in vivo and possess 4-day cells. CBA/J (C4L) mice injected with purified C4 preparations from the C4H mice BALB/c, lose 4-day cells and show a short-term contact-sensitivity reaction, exactly as BALB/c mice, thus indicating that C4 levels play a role in the control of contact-sensitivity reaction to simple chemical haptens.