Objective: The antigen-presenting lectin-like receptor complex (APLEC) was recently identified as a genetic determinant for arthritis susceptibility. We undertook this study to define mechanisms underlying the impact of APLEC on arthritis, to determine whether sex effects occur, and to determine whether APLEC influences different types of arthritis and phenotypes other than susceptibility.
Methods: Arthritis-susceptible DA rats were compared with sex-matched congenic rats in which APLEC alleles were substituted with alleles from arthritis-resistant PVG rats. Six different arthritogenic agents were injected at the base of the tail: Freund's incomplete adjuvant, pristane, squalene, killed mycobacteria, yeast beta-glucan, or rat type II collagen (CII). Arthritis was visually scored, body weight was measured, and anti-CII IgG and cytokine messenger RNA (mRNA) levels were determined by enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction, respectively.
Results: In 5 models of rheumatoid arthritis (RA), congenic rats deviated profoundly from DA rats by having reduced arthritis susceptibility, delayed onset, decreased severity, and/or reduced body weight loss. Paradoxical opposite genetic effects were noted, including a more severe disease course in congenic males in pristane-induced arthritis and decreased clinical signs in collagen-induced arthritis despite increased autoantibody levels. Interestingly, the anti-CII IgG isotype profile was skewed in congenic rats, and markedly reduced lymph node mRNA levels for interleukin-17 suggested that the cytokine profile of autoreactive T helper cells was also skewed in a less pathogenic direction.
Conclusion: Rat APLEC regulates autoimmunity and multiple phenotypes in several types of arthritis. However, delineating the genetic impact may require stratification for sex or mode of arthritis induction. This pathogenetic complexity should be considered when evaluating APLEC in inflammatory and autoimmune diseases, including RA.