Surface antigen changes accompanying lymphocyte activation. Selective reactivity of certain anti-H-2 antisera with activated lymphocytes of unrelated H-2 haplotype.

It is here shown that some noncongenic anti-H-2 antisera produced by using normal spleen cells at the immunogen can contain cytotoxic antibody activity against activated, but not resting, lymphocytes of unrelated H-2 haplotype strains. Reactivity was noted against lymphocytes activated in vitro with T- or B-cell mitogens, or in vivo by antigenic stimulation. Analysis of the results indicated that the anti-activated lymphocyte activity was most likely related to production of anti-Ala-1 ('activated lymphocyte antigen') alloantibodies. This appears to occur as a result of donor lymphocyte activation during production of the anti-H-2 antisera, using Ala-1-incompatible donor and recipient combinations, where the donor cells are competent to recognize and react against host H-2 incompatibilities. These results confirm the finding that lymphocyte activation can be accompanied by the expression of an antigen that is either absent or weakly expressed on resting lymphocytes.