POSSIBLE INVOLVEMENT OF C5 C5A IN THE EFFERENT AND ELICITATION PHASE OF CONTACT SENSITIVITY/

The elicitation of 24-h contact sensitivity (CS) in mice requires a se rotonin-dependent, 2-h response called CS initiation. We studied the r ole of complement (C) by comparing CS in DBA/1 (C5-normal) vs DBA/2 (C 5-deficient) mice and found impaired 2-h, but not 24-h, CS. We showed previously that 2-h responses represent CS initiation and are required for elicitation of 24-h responses. Treatment of C5-deficient mice wit h absent macroscopic responses (ear swelling) with a selective seroton in antagonist inhibited 24-h CS, suggesting that C5-deficient mice had submacroscopic (i.e., microscopic), serotonin-dependent CS initiation . When normal mouse serum was used as a source of C5 to reconstitute C 5-deficient mice, significant 2-h responses were restored. Furthermore , heat treatment of normal mouse serum to inactivate C abrogated resto ration of 2-h responses. Thus, C5 was suggested to be involved in CS i nitiation. Using a suboptimal immunizing dose of Ag revealed an impair ed 24-h component of CS in DBA/2 mice, but not in DBA/1 mice, and also in C5-deficient B10.D2/o mice compared with C5-normal B10.D2/n mice w ith a suboptimal eliciting dose of Ag. Again, reconstitution of B10.D2 /n mice with normal mouse serum restored deficient 24-h CS responses. Thus, 2-h and classical 24-h CS probably depend in part on C5. These r esults imply that C5 may play a role in the elicitation of 24-h CS, pr obably via required preceding CS initiation.