Studies on hypersensitivity. III. The relation between delayed reactivity to the picryl group of conjugates and contact sensitivity.

In order to clarify the relationship between contact sensitivity and those other forms of cellular sensitivity manifested by delayed reactions to intradermal injections, a study has been made of the production of contact and delayed reactivity and of specific antibodies against the picryl' (tri-nitrophenyl) group in guinea pigs. Firstly, a quantitative passive immunization experiment, using anti-picryl antisera derived both from guinea-pig and rabbit, reaffirms the contention of previous workers that circulating antibodies are not involved in the contact reaction. It is found that, after active immunization with rather large (1 mg.) doses of picryl proteins, pure cellular reactivity to the picryl group is regularly demonstrable for a day or more before antibody production against that group occurs. This is evidenced by the production of a typical delayed reaction in response to the injection of a fairly large (0.2 mg.) dose of a picryl conjugate other than that used for immunization. Such animals frequently show typical contact sensitivity to picryl chloride. Similarly animals sensitized with picryl chloride regularly show delayed reactions to this dose of picryl conjugate, at a time before antibodies of any sort appear. Use of conjugates with homologous proteins or with mycobacteria is shown to lengthen this phase of pure cellular sensitivity preceding antibody production. Animals sensitized with the simple chemical tend to react more strongly to contact than to intradermally injected conjugate. In contrast, animals sensitized with the conjugate give poorer contact reactions, as compared with their delayed intradermal reactions. Use of homologous conjugates reduces but does not abolish this contrast. It appears that the two kinds of immune stimulus, though both occasioned by the picryl group, behave as cross-reacting' systems; possible reasons for this are discussed. The quantitative data militate against the hypothesis that cellular sensitivity is a necessary stage in antibody production.