Circulating immune complexes and analysis of renal immune deposits in feline immunodeficiency virus‐infected cats

Total immunoglobulin content and concentration of immune complexes (IC) were determined in the sera of 51 cats infected with feline immunodeficiency virus (FIV) and of 40 controls. IgG and IgM were quantified by radial immunodiffusion and circulating IC (CIC) by the CIC‐conglutinin assay. IgG fractions were obtained by acid elution from kidney tissues of 15 FIV‐infected and five negative control cats to investigate the possible role of IC in the genesis of renal damage observed in infected animals. Mean concentrations of IgG and circulating IC were higher in FIV‐infected cats than in controls (29·6±6·7 versus 23·0±1·9 mg/dl (mean±s.d.) P < 0001; and 66·5 ± 17·0 versus 27·4 ± 19·9% I, P < 0·001, respectively), while IgM levels were only slightly increased (0·9 ± 0·05 versus 0·87 ± 0·04 mg/dl, P < 0·02). Immunoglobulin fractions were eluted from 10 of the 15 renal tissue samples from FIV‐infected cats and were found to be polyclonal and at least partly specific for FIV antigens. These findings confirm the presence of a B cell activation in FIV‐infected cats and demonstrate the presence of high levels of CIC in their sera. The presence of immune deposits in renal tissues suggests that IC might play a role in the pathogenesis of the renal damage observed in FIV‐infected cats.

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