Evidence for excessive Th2 CD4+ subset activity in vivo

Area of Science:

• Immunology
• Cellular Biology
• Molecular Medicine

Background:

• The in vivo existence and function of distinct T helper 1 (Th1) and T helper 2 (Th2) CD4+ T cell subsets remain debated.
• Understanding in vivo T cell subset function is crucial for diagnosing and treating immune-mediated diseases.

Observation:

• A patient presented with laboratory findings suggestive of high T helper 2 (Th2) cell activity, including elevated IgG4, IgE, and eosinophilia.
• Patient peripheral blood lymphocytes (PBL) induced heightened IgG4 and IgE production in normal B cells, indicating T cell-driven immunoglobulin production.
• Flow cytometry and RNA in situ hybridization revealed an expanded CD4+Leu-8+CD45RA- memory-effector T cell population in the patient, enriched for interleukin-4 (IL-4) transcription.

Findings:

• Activated patient PBL secreted significantly higher levels of IL-4 and IL-5, and lower levels of IL-2, compared to controls, with similar interferon-gamma (IFN-γ) levels.
• Semiquantitative reverse polymerase chain reaction confirmed increased IL-4 and IL-5 mRNA expression in patient PBL.
• The expanded CD4+Leu-8+CD45RA- population showed a 2:1 ratio of IL-4-transcribing to IFN-γ-transcribing cells, confirming the in vivo presence of functional Th2 cells.

Implications:

• These findings provide strong evidence for the in vivo existence and functional activity of Th2 cells.
• The expanded Th2 cell population and its excessive cytokine production may contribute to the patient's sinopulmonary pathology.
• This study advances our understanding of T cell subset dynamics in human disease and has potential implications for targeted immunotherapies.