Proliferative response of human lymphocytes to antigens not experienced in vivo

A comparison has been made of two methods for studying the immune response of human lymphocytes to antigens not experienced in vivo. In the first method, the sensitization-restimulation assay (or S/R test), lymphocytes from blood were sensitized to antigen in bulk cultures and then redistributed into microtiter plates for a second culture period in the presence of specific or unrelated antigen. The proliferative response of the sensitized cells in the second culture was measured by 3H-thymidine uptake. With this protocol one could strictly control the specificity of the response in the second culture by using different antigens in the sensitization and restimulation phases of the assay. An alternative method for studying the response of lymphocytes to antigens not experienced in vivo was an adaptation of the lymphocyte transformation assay by extending the time of culture for up to four days. We found that this latter assay was not appropriate for determining if individuals were nonresponders to antigens not experienced in vivo. Limiting dilution analysis showed that the frequency of antigen reactive cells was so low that nonrandom distribution of reactive cells was obtained and the frequency of reactive cells depended on the concentration of antigen used in the cultures. Further it was impossible to adequately control for the specificity of the response.