Selection of thymocyte MHC restriction specificity in vitro

Area of Science:

• Immunology
• Cell Biology

Background:

• The thymus generates T cells specific for self-major histocompatibility complex (MHC) molecules.
• The in vivo mechanism of this T cell commitment to self-MHC is not fully understood.
• In vitro studies show thymocyte proliferation in response to self-MHC, but functional significance is unclear.

Purpose of the Study:

• To investigate the functional capacity and MHC restriction of T cells generated in vitro from thymocytes.
• To determine if in vitro priming influences the MHC specificity of thymocytes.
• To analyze the antigen and MHC restriction specificity of T-helper cells derived from thymocyte cultures.

Main Methods:

• Coculturing thymocytes with irradiated syngeneic accessory cells.
• Testing recovered T cells for T-helper function in antigen-dependent B cell antibody responses.
• Analyzing MHC restriction by culturing F1 thymocytes with F1 or parental accessory cells.
• Utilizing monoclonal antibody blocking studies to identify critical molecules (e.g., Ia).
• Adoptive transfer of helper cells into irradiated hosts.

Main Results:

• Functional T-helper cells were generated from thymocyte cultures, supporting B cell antibody responses.
• The MHC restriction of T-helper cells was determined by the MHC genotype of the accessory cells used in primary culture.
• Ia molecules were critical for establishing MHC restriction.
• T-helper cells retained their in vitro-imposed restriction specificity after adoptive transfer and priming in a different MHC environment.
• Carrier antigen-specific, MHC-restricted priming of thymic T-helper cells was detectable.

Conclusions:

• Functional T-helper cells can be selected and amplified from thymocyte cultures.
• The MHC restriction specificity of these T-helper cells is determined in vitro by the accessory cell environment.
• This in vitro system provides a model for studying T cell commitment and MHC restriction in the thymus.