ICOS
Overview
ICOS (Inducible T-cell COStimulator, CD278) is a co-stimulatory receptor of the CD28 superfamily expressed on activated T cells. ICOS signalling through its ligand ICOS-L (B7-H2) is critical for T follicular helper (TFH) cell differentiation, germinal center maintenance, and T cell-dependent antibody responses. In flow cytometry panels, ICOS expression on CD4⁺ T cells is used as a marker of TFH activation.
Key Points from Literature
- CD4⁺ICOS⁺ TFH cells diminished in COVID-19 lymphoid tissue: Multi-color immunofluorescence of post-mortem COVID-19 lymph nodes and spleens showed diminished CD4⁺ICOS⁺ TFH cells compared with non-COVID controls. This reduction was part of a broader TFH differentiation block: CD4⁺CXCR5⁺ pre-GC TFH cells were present but reduced, and CD4⁺Bcl-6⁺ GC-type TFH cells were near-absent. ICOS⁺ TFH depletion occurred alongside TH1 (T-bet⁺) expansion and aberrant TNF-α accumulation (see Kaneko2020 - GC Loss and TFH Block in COVID-19, n=11 COVID + controls, multi-color immunofluorescence).
Contradictions & Debates
None documented in current wiki sources.
Related Pages
Bcl-6, CXCR5, Germinal Center, T-bet, TNF-alpha