V. Tempo and Specificity of the Proliferative Response and the Number of Reactive Cells :from Immunized Donors* by Darcy

Extensive studies of the mixed lymphocyte interaction (MLI) 1 have shown it to be an immunologically specific proliferative reaction in which a large proportion of immunologically competent, predominately thymus-derived, circulating lymphocytes from nonimmunized donors recognize and respond to the presence of major histocompatibility (H) isoantigens in culture (1-7). Prior immunization of the cell donors is known to alter the time course of the subsequent proliferative response in the MLI (2, 3, 8) but little is known of (a) the specificity and (b) the duration of the altered proliferative capacity, (c) the influence of different routes of antigen administration, and (d) whether the proportion of potentially responsive lymphocytes is also changed. In the present study, we undertook an examination of these various parameters with the following results: (a) Subcutaneous immunization accelerates the tempo of the proliferative response, whereas antigen given systemically decreases it. (b) The altered proliferative behavior is specific for the immunizing antigens. (c) The period after immunization during which the MLI displays an altered tempo is comparatively short-lived, lasting not longer than 2-3 wk. (d) The same proportion of lymphocytes are stimulated to respond in the MLI whether they are derived from immunized donors or from normal donors, even though the response profile is different.