Studies on the effect of mycobacterial antibodies on skin-test reactivity to M. tuberculosis.

The effect of sensitization with mycobacterial antisera on skin-test reactivity to soluble PPD, glutaraldehyde-aggregated PPD and M. tuberculosis H37Ra, killed by u.v. light, was studied in rats and guinea pigs. The mycobacterial antisera used had either been raised in guinea pigs or were obtained from tuberculous patients, while the majority of experimental animals had been immunized with Freund's complete adjuvant (FCA). Swelling, erythema and the histology of the skin-test reactions were recorded. The i.v. injection of 0.3 ml of guinea pig antiserum (haemagglutination titre 2048) caused a decrease in skin swelling in response to aggregated PPD and M. tuberculosis in both FCA-immunized and unimmunized rats. Injection of 0.3 ml human serum showing a titre higher than 32 had the same effect. Such sera were only found in non-Caucasian patients. No changes were observed in the erythema and cell composition of the suppressed reactions. Skin-test reactivity to soluble PPD was not affected by this type of passive humoral sensitization. I.v. injection of a higher dose—1.0 ml—of antiserum into FCA-immunized rats caused an increase in the swelling of skin-test reactions to,M. tuberculosis. This enhanced reaction reached its peak 5 h after antigen injection. In FCA-immunized guinea pigs we were not able to obtain any change in skin-test reactivity following the serum transfer. In conclusion, mycobacterial antibodies are able to influence the intensity of skin-test reactions to antigens derived from M. tuberculosis. Suppression and enhancement may occur, depending on the structure of the antigen used and the quantity of antibody injected. When studying immune reactivity in tuberculosis one must be aware of these complex interactions.