Functional Evidence for Two Antigen Presentation Sites for a Single I-A Molecule
The recognition of soluble antigen by T cells has been shown to be restricted by la molecules on antigen-presenting cells (APC). Utilizing complementary pairs of T cell helper clones reactive with the synthetic terpolymer GAT (glutamic acid60-alanine30-tyrosine10) derived from (C57BL/6x A/J)F1 mice (B6A), it has been possible to show that there exist at least two separate antigen restriction/presentation sites per I-A molecule.
The mouse major histocompatibility complex has long been thought to regulate many aspects of the immune response. It is now known that I region gene products are no longer just associated with immune responses: the products are the actual proteins involved in the genetically restricted reactions between T cells and macrophages (1). Proliferative T cells respond in vitro to antigen only in the context of I-A or I-E region gene products on antigen presenting cells (2,3). Antigen-reactive T cell clones derived from F1 mice have been shown to be restricted by I region products from either parental strain or, in some cases, to a unique antigen presenting determinant present only in F1 mice (2,3).
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