Extrathymic CD4/CD8 double positive T cells

Area of Science:

• Immunology
• Cell Biology
• T lymphocyte research

Background:

• Mature T cells are typically classified as CD4+ or CD8+.
• CD4/CD8 double-positive (DP) T cells are unconventional lymphocytes that challenge this binary classification.
• DP T cells are found in various species, including swine, chickens, monkeys, humans, and rats, with varying prevalence.

Purpose of the Study:

• To review the evidence for extrathymic CD4/CD8 DP lymphocytes across species.
• To investigate the characteristics and potential functional significance of DP T cells.
• To challenge the traditional view of mutually exclusive CD4 and CD8 expression on T cells.

Main Methods:

• Review of existing literature and reports on CD4/CD8 DP lymphocytes.
• Phenotypic analysis of lymphocytes in swine, monkeys, and other species.
• Comparison of DP T cell characteristics across different species.

Main Results:

• Significant numbers of CD4/CD8 DP lymphocytes exist in swine, chickens, and monkeys.
• DP T cells can be found in human peripheral blood, especially during disease or inflammation.
• Porcine DP T cells are predominantly MHC class II restricted memory CD4+ helper T cells that acquire CD8alpha expression post-activation.

Conclusions:

• CD4/CD8 DP T cells represent a distinct, primed T cell subset in swine, humans, and monkeys.
• These cells exhibit memory characteristics, including antigen recall response and interferon-gamma production.
• The simultaneous expression of CD4 and CD8 co-receptors on mature T cells warrants further functional investigation.