Background Annexin-1 (ANXA1, lipocortin 1) is a pleiotrophic protein produced by many cell types including peripheral blood leucocytes. Although it has been shown to inhibit ‘macroscopic’ inflammatory processes in animal models, its direct effects on antigen-activated human T cells have not been studied.
Objective To test the hypothesis that ANXA1-derived peptides inhibit antigen-driven prototype Th1 and Th2-type human T cell responses of clinical relevance and lectin-driven responses in vitro.
Methods Peripheral blood mononuclear cells (PBMC) were isolated from 14 atopic subjects sensitized to house dust mite allergen (Dermatophagoides pteronyssinus, Der p) and purified protein derivative (PPD) of Mycobacterium tuberculosis. PBMC (1 × 106/mL) were cultured with phytohaemagglutinin (PHA; 5 µg/mL; 4 days), Der p (25 µg/mL; 6 days), PPD (10 µg/mL, 6 days) or medium control. Two ANXA1-derived peptides, Ac2–26 and AF-2 (5–500 µm), were assessed for possible inhibition of PHA-and antigen-induced T cell proliferation (measured by 3H-thymidine uptake), while Ac2–26 was assessed for inhibition of Der p-induced interleukin (IL)−5 release and PPD-induced interferon-γ (IFN-γ) release (measured by ELISA). Comparison was made with dexamethasone as an established inhibitory control. Endogenous production by PBMC of cell surface-associated and intracellular ANXA1 in response to PHA, Der p and PPD in the presence and absence of dexamethasone was measured by specific ELISA.
Results Both PHA- and antigen-induced T cellular proliferation were inhibited by dexamethasone. Although neither ANXA1-derived peptide significantly altered PHA-induced proliferation, both effected concentration-dependent reductions in antigen-induced proliferation, Ac2–26 being the more potent. Peptides of identical amino acid composition to Ac2–26 and AF-2, but of random sequence, were ineffective at equivalent concentrations. In addition, Ac2–26 and dexamethasone inhibited Der p-induced IL-5 release and PPD-induced IFN-γ release in a concentration-dependent fashion. Endogenous ANXA1 was detectable in PBMC, but at concentrations approximately 104-fold lower, in molar terms, than the effective concentrations of the exogenously added, ANXA1-derived inhibitory peptides. Endogenous production was not significantly altered by any of the T cell stimuli employed in this study, in the presence or absence of dexamethasone.
Conclusion In prototype Th1 and Th2-type human T cell responses, ANXA1-derived peptides can inhibit antigen-driven cellular proliferation and cytokine production.