A histoautoradiographic study of the localization of antigen and specific antibodies in the rabbit spleen. I. Comparison of the primary and secondary immune response.

The localization of antigen (chicken serum albumin) and specific antibodies in sections from the spleens of rabbits after primary and secondary immunization was studied by means of histoautoradiography. After primary immunization, both antigen and antibodies were demonstrated in the lymphoid follicles consistently between 3 and 42 days after injection. Antigen was detected in addition in the marginal zone on the 5th day, and antibody-forming cells in the marginal zone and periarteriolar lymphocyte sheaths between 3 and 9 days after immunization. After secondary immunization, follicular antigen trapping was detected as early as 2 hours after injection, reaching a peak in the follicles and marginal zone on the 3rd day after immunization. At later periods of time the presence of antigen in the follicles was less prominent than that of specific antibodies. The numbers of antibody-forming cells were 10-100-fold higher in the secondary than in the primary response. The findings are discussed in relation to the role of antigen-antibody complex in the lymphoid follicles in the development of the capacity to produce the secondary type of immune response.