A biphenotypic lymphocyte subset displays both T- and B-cell functionalities.

Area of Science:

• Immunology
• Cell Biology
• Hematology

Background:

• Mixed phenotypic lymphocytes (T/B cells) are known in disease but their physiological role is unclear.
• Understanding these cells is crucial for comprehending normal immune system function.

Purpose of the Study:

• To investigate the existence and characteristics of T/B phenotypic lymphocytes in physiological conditions.
• To determine the origin, distribution, and functional capabilities of these biphenotypic lymphocytes.

Main Methods:

• Flow cytometry to identify lymphocyte subsets expressing both T-cell (CD3+) and B-cell (CD19+) markers.
• Functional assays assessing activation via T-cell receptor (TCR) and B-cell receptor (BCR) signaling.
• Analysis of cytokine production (IL-2, TNF-α) and participation in immune responses post-vaccination.

Main Results:

• Identified a novel lymphocyte subset (CD3+CD19+) in mice, predominantly of pro/pre-B cell origin.
• These cells are distributed in bone marrow, lymphoid organs, and blood, and are responsive to TCR/BCR stimulation.
• Biphenotypic lymphocytes contribute to humoral and cellular immunity, with distinct cytokine profiles (higher IL-2, lower TNF-α) compared to conventional T cells.
• An analogous subset exists in human peripheral blood mononuclear cells (PBMCs), though less frequent.

Conclusions:

• T/B phenotypic lymphocytes are a naturally occurring subset in mice, originating from B-cell precursors.
• These cells possess functional plasticity, participating in adaptive immunity and exhibiting unique cytokine secretion patterns.
• The presence of similar cells in humans suggests a conserved role in mammalian immune systems.