HLA class I specific T lymphocyte clones with dual alloreactive functions

Area of Science:

• Immunology
• Cellular immunology
• Transplantation immunology

Background:

• Class I Human Leukocyte Antigen (HLA) molecules play a crucial role in immune responses.
• The mixed lymphocyte culture (MLC) assay is a standard method for detecting T cell alloreactivity.
• Previous studies mapped MLC stimulating determinants to the HLA-A and B regions, but the exact molecules involved were debated.

Purpose of the Study:

• To isolate and characterize human T lymphocyte clones responding to class I HLA antigens.
• To investigate the role of class I HLA molecules as direct stimulators in MLC.
• To determine if the determinants triggering T cell proliferation are distinct from serologic allospecificity determinants.

Main Methods:

• Isolation of T lymphocyte clones from in vitro mixed lymphocyte culture (MLC).
• Phenotypic analysis using Leu-2 and Leu-3 markers.
• Proliferation assays in response to specific HLA antigens (HLA-A2, HLA-B8).
• Cytotoxicity assays against target cells.
• Blocking studies using monoclonal antibodies against class I HLA molecules.

Main Results:

• Four T lymphocyte clones were isolated, with three showing Leu-2+3- phenotype and responding to HLA-B8, and one showing Leu-2-3+ phenotype and responding to HLA-A2.
• These clones exhibited cytotoxic activity against cells expressing the same target HLA antigens.
• Monoclonal antibody blocking studies indicated that proliferation was induced by determinants on the class I molecule itself.
• These triggering determinants were found to be spatially close to serologic allospecificity determinants.

Conclusions:

• Class I HLA molecules directly stimulate T lymphocytes in MLC.
• The T cell receptor recognizes determinants on the class I molecule that are closely associated with serologic specificities.
• These findings support the hypothesis that class I HLA molecules are the weak MLC-stimulating determinants within the HLA-A and B regions.