Effect of column purification on response of lymphocytes in mixed leucocyte cultures (MLC) and to blastogenic media deprived from MLCS.

The uptake of tritiated thymidine by column-purified lymphocyte, phagocyte-restored column-purified lymphocyte, and unpurified leucocyte suspensions was measured in mixed donor cultures and in single donor cultures containing blastogenic media derived from mixed cultures. Results showed that in mixed cultures unpurified leucocyte suspensions had significantly higher uptakes of tritiated thymidine than the corresponding purified lymphocyte suspensions, and that the addition of phagocytes to purified lymphocytes restored the uptake to a level not significantly different from that of the unpurified suspensions. In suspensions cultured with blastogenic media there was no significant difference between the types of suspensions and, further, the addition of phagocytes tended to depress the response of pure lymphocyte suspensions. It is suggested that phagocytes, probably macrophages, may act as foci favouring cell–cell interaction in the mixed leucocyte cultures, but it is also possible that purified lymphocytes may be less responsive in these cultures owing to the selective loss of antigen-sensitive or facilitating lymphocytes during column purification. In the cultures containing blastogenic media, the stimulating factors, possibly including free leucocyte antigens, interact directly with the lymphocytes and no synergistic effect is produced by the presence of phagocytes.