EVIDENCE THAT SURFACE-PROTEINS SN14 AND SN16 OF SARCOCYSTIS-NEURONA MEROZOITES ARE INVOLVED IN INFECTION AND IMMUNITY

Sarcocystis neurona is the etiologic agent of equine protozoal myeloen cephalitis (EPM). Based on an analysis of 25,000 equine serum and cere brospinal fluid (CSF) samples, including samples from horses with neur ologic signs typical of EPM or with histologically or parasitologicall y confirmed EPM, four major immunoblot band patterns have been identif ied. Twenty-three serum and CSF samples representing each of the four immunoblot patterns were selected from 220 samples from horses with ne urologic signs resembling EPRI and examined for inhibitory effects on the infectivity of S. neurona by an in vitro neutralization assay. A h igh correlation between immunoblot band pattern and neutralizing activ ity was detected. Two proteins, Sn14 and Sn16 (14 and 16 kDa, respecti vely), appeared to he important for in vitro infection. A combination of the results of surface protein labeling, immunoprecipitation, Weste rn blotting, and trypsin digestion suggests that these molecules are s urface proteins and may be useful components of a vaccine against S. n eurona infection. Although S. neurona is an obligate intracellular par asite, it is potentially a target for specific antibodies which may ly se merozoites via complement or inhibit their attachment and penetrati on to host cells.