The role of non-specific lymphocytes in antigen-induced proliferative response in vitro

Abstract

The antigen-induced proliferative response of lymph node cells from immunized mice is proportional to the number of primed lymphocytes in the microtiter wells. Addition of normal lymphocytes did not alter the magnitude of the antigen-specific [ 3H]TdR uptake of immune lymph node cells. In contrast, normal lymphocytes increased the antigen-specific thymidine incorporation of enriched populations of antigen-specific lymphocytes. This enhancing effect was especially pronounced, and proportional to the number of supplementing unsensitized lymphocytes, with a small cell number of enriched lymphocytes, where the specific responsiveness could barely be detected without addition of normal lymphocytes. Enriched populations derived through adherence to antigen-pulsed macrophages (‘selected’ cultures) as well as those obtained by growing immune lymph node cells with antigen-pulsed macrophages (‘supernatant’ cultures) had an improved proliferative response after addition of normal lymphocytes. However, the proliferative response of the ‘selected’ cultures was extremely dependent on normal lymphocytes as they could express only 10% of their full stimulatory capability in the absence of the latter. This indicates that the blastogenic signal delivered by the activated specific T cells recruits normal lymphocytes which do not adhere to the antigen-pulsed macrophages. Under the same conditions the recruiting signal is incapable of inducing the multiplication of antigen-sensitized cells. The potential recruitable uncommitted lymphocytes are present in excess among immune lymph node cells, while depleted from the ‘selected’ cultures. The enriched ‘supernatant’ cultures seem to contain considerable numbers of recruitable lymphocytes although they are present in quantities less than are required to provide for the full amplifying signal. This meaning of these findings for the evaluation of enrichment of antigen-specific T cells and of antigen-induced response based on [ 3H]TdR uptake is discussed.