Quantification of antigen-reactive cells among human T lymphocytes

Area of Science:

• Immunology
• Cellular Immunology
• T lymphocyte research

Background:

• Human peripheral blood T lymphocytes play a crucial role in adaptive immunity.
• Quantifying antigen-specific T cells is essential for understanding immune responses and developing vaccines.
• Previous methods for estimating T cell frequencies have limitations in precision and scope.

Purpose of the Study:

• To estimate the frequency of antigen-reactive T cells in human peripheral blood.
• To determine the frequency of memory T cells specific for bacterial antigens (tuberculin PPD and tetanus toxoid).
• To assess the frequency of alloantigen-reactive T cells and compare it with antigen-specific T cells.

Main Methods:

• Limiting dilution analysis was employed to quantify antigen-reactive T lymphocytes.
• Antigen-induced lymphocyte activation was measured via tritiated thymidine ([3H]dThd) incorporation.
• Frequencies were calculated for T cells responding to PPD, tetanus toxoid, and alloantigens across multiple donors.

Main Results:

• Frequencies of PPD-reactive T cells ranged from 1:300 to 1:16,000 across 11 donors.
• Frequencies of tetanus toxoid-reactive T cells ranged from 1:750 to 1:11,500 in 5 donors.
• Alloantigen-reactive T cells were more frequent, ranging from 1:200 to 1:600 (n=10).
• Reproducible frequency estimates were observed over several months for 3 donors.
• A correlation was found between PPD-reactive T cell frequency and [3H]dThd incorporation.

Conclusions:

• Limiting dilution analysis provides a reliable method for estimating antigen-reactive T cell frequencies.
• The frequency of T cells specific for bacterial antigens is lower than that for alloantigens.
• These findings contribute to a better understanding of T cell repertoire and immune memory in humans.