Human T Cell Ia Antigens Defined by Monoclonal Antibodies

Abstract

In the past few years the study of T cell surface antigens and their relationship to functional sets of cells has been a prominent research area in human immunology. Using monoclonal antibodies, many different markers have been identified and used to dissect peripheral blood T cells in subsets with different functions. For instance, helper T cells bear the antigens recognized by OKT4,¹ 3A1,² and 5/9³ monoclonal antibodies (mabs), while the suppressor/ cytotoxic subset is recognized by the OKT8/T5 mabs.⁴ Other markers can be used to identify activated T cells, as they are expressed only by T cells (regardless of their function) activated by various stimuli. MLR1, 2, 3, 4,5 and 4F2⁶ are typical examples of mabs reacting with such antigens. A third class of antigens expressed by human T cells are the so called “Ia antigens”. These are products of the genes of the Major Histocompatibility Complex (MHC) first recognized primarily on B lymphocytes and macrophages by alloantisera from pregnant women.⁷ Later it became apparent that a small percentage of peripheral blood T cells express Ia antigens.⁸ Now it is known that a considerable increase of Ia positive T cells takes place in vitro when T lymphocytes are stimulated with mitogens or during mixed lymphocyte reaction (MLR),⁹ or in vivo in several diseases in which activation of T cells occurs, such as mononucleosis,¹⁰ graft vs host disease,¹¹ and “autoimmune” diseases such as Systemic Lupus Erythematosus (SLE),¹² Hashimoto’s disease,¹³ Graves’ disease¹⁴ and diabetes mellitus.¹⁵