Objective: To investigate the indirect effects of anti-CD4 treatment on the functions of macrophages (CD4– in mice) in the acute and early chronic phase of mouse antigen induced arthritis (AIA).
Methods: C57BL/6 mice with AIA were treated intraperitoneally with the anti-CD4 mAb GK1.5 or control rat IgG on days –1, 0, 1, 3, 5, and 7. Proinflammatory cytokines (IL1ß, IL6, and TNFα) were quantified by sandwich ELISA in joint extracts, serum, and supernatants of ex vivo stimulated spleen/lymph node cells or peritoneal macrophages (+LPS/IFNγ). Nitric oxide (NO) levels in supernatants of ex vivo stimulated peritoneal macrophages were measured by the Griess reaction. Proteolytic activity in joint homogenates was analysed by gelatin, casein, and elastin zymography, and substrate assays.
Results: Anti-CD4 treatment significantly reduced joint swelling in acute (days 3, 5) and early chronic AIA (day 7) and diminished inflammation and destruction scores in late chronic AIA (day 21). On day 3, anti-CD4 treatment significantly reduced IL6 levels in all compartments. IL1ß was reduced in joint extracts, unaffected in serum or cells from lymphoid organs, and increased in stimulated peritoneal macrophages. TNFα was significantly increased in the joints, decreased in serum, and otherwise unchanged. NO production by stimulated peritoneal macrophages was significantly reduced by anti-CD4 treatment. Lower activity of matrix metalloproteinases and neutrophil elastase was seen in joint extracts of anti-CD4 treated animals than in IgG treated AIA controls.
Conclusion: CD4+ T cell directed treatment had strong local and systemic effects on macrophages. These indirect effects may contribute to the reduction of destructive mediators/joint destruction in AIA.