Hypermetabolism, observed in Sydenham's chorea (SC); a complication of acute rheumatoid fever (ARF) involving binding of streptococcal M protein antibodies in the brain, may result from an increase in glutamate release. The interaction of mAb 1 OF5, a specific M protein antibody subtype, with brain proteins (e.g. Rabphilin-3A), synaptic vesicles (SVs) and synaptosomal fraction (SF) was examined. Rat brain slices immunostained with mAb l OF5 revealed an interaction with choroid plexus and elements appearing to be neuropils. Dot blotting demonstrated an interaction of mAb I OF5 with both SVs and SFs. Western blotting revealed a smear from mAb 10F5 against the SF fraction. However, both modified SVs and pure liposomes examined by fluorescent and confocal microscopy bound mAbl0F5 suggesting a direct interaction with phospholipids. ELISA demonstrated binding of mAb1OF5 with negatively charged phospholipids involved in antiphospholipid syndrome (APS). Hypermetabolism and binding at the choroid plexus is observed in SC and APS supporting the connection between these disorders. / Department of Physiology and Health Science