Expression of CTLA-4 by human monocytes

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Cytotoxic T lymphocyte-associated molecule-4 (CTLA-4) is a key regulator of T cell-mediated immune responses.
• CTLA-4 functions by interacting with CD80/CD86 ligands on antigen-presenting cells, inhibiting T cell activation.
• The expression and function of CTLA-4 in non-T cells, particularly monocytes, remain less understood.

Purpose of the Study:

• To investigate the constitutive and inducible expression of CTLA-4 in human monocytes.
• To explore the functional consequences of CTLA-4 ligation on monocyte activation and signaling.

Main Methods:

• Flow cytometry was used to detect cell surface and intracellular CTLA-4 expression in monocytes.
• Monocyte-like cell lines (U937, THP-1) were utilized to study CTLA-4 expression and function.
• Stimulation with interferon-gamma (IFN-γ), phorbol 12-myristate 13-acetate (PMA), and Staphylococcus aureus Cowan I strain (SAC) was employed.
• Antibody-mediated CTLA-4 ligation was performed to assess effects on cell proliferation, surface marker expression, and transcription factor activation (AP-1, NF-κB).

Main Results:

• Human monocytes constitutively express CTLA-4, with higher intracellular than surface expression.
• CTLA-4 cDNA sequences in monocytes are identical to those in T cells.
• IFN-γ stimulation induced secretion of soluble CTLA-4 by monocytes.
• PMA and IFN-γ upregulated CTLA-4 expression, partially inhibited by staurosporine (PKC inhibitor).
• CTLA-4 ligation on U937 cells inhibited proliferation and upregulation of CD86, CD54, HLA-DR, and HLA-DQ.
• CTLA-4 ligation suppressed PMA-induced AP-1 and NF-κB activation in U937 cells, indicating inhibitory signaling.

Conclusions:

• CTLA-4 is constitutively expressed by human monocytes, extending its known regulatory role beyond T cells.
• Monocyte-expressed CTLA-4 can be modulated by inflammatory stimuli and PKC signaling.
• Ligation of monocyte CTLA-4 exerts inhibitory effects on cell activation and signaling pathways, suggesting a role in immune regulation.