Intrathecal Synthesis of IgG in Simian Immunodeficiency Virus (SIV)-Infected Rhesus Macaques ( Macaca mulatta )

We examined cerebrospinal fluid (CSF) and serum from 25 simian immunodeficiency (SIV)-infected rhesus macaques for the presence of SIV-specific immunoglobulin G (IgG) and for intrathecal synthesis of IgG. SIV-specific IgG was present in CSF from almost 50% of the macaques. In approximately half of these animals the SIV-specific IgG appeared to be derived from serum by leakage across a disrupted blood-brain barrier, whereas in the remaining animals there was evidence of intrathecal IgG synthesis. There were no significant associations between CSF SIV-specific IgG, intrathecal IgG synthesis and isolation of virus from CSF, clinical status, or neuropathological findings. However, SIV-specific IgG was absent from CSF in all four of the macaques with SIV encephalitis. The presence of SIV-specific IgG in CSF may have a modulating effect on the development of SIV-associated neurological disease.