Abstract 1008 Poster Session IV, Tuesday, 5/4 (poster 153)

Coxsackievirus B3 (CB3) is an RNA virus responsible for 1/3-1/2 of reported cases of myocarditis for which an etiologic agent can be determined. A 5′ nontranslated regulatory region (5'NTR) (approx. 740 nts) precedes the capsid coding region (2,553 nts). Research directed at determining the cardiovirulence (myocarditis) determinant of CB3 have relied on lab strains and their adapted progeny. With these, cardiovirulence determinants have been variously identified in the CB3 5′NTR and capsid. Recently, the validity of conclusions concerning cardiovirulence determinants derived from study of CB3 lab strains, as applied to naturally-occurring isolates, has been questioned. No attempt has been made to identify cardiovirulence determinants in CB3 clinical strains. We have undertaken to identify CB3 cardiovirulence determinants using clinical isolates.

Two clinical CB3 isolates whose cardiovirulence phenotypes had been determined in a murine model were selected for study. The AS strain was chosen as a cardiovirulent strain and the CO strain as a noncardiovirulent strain. These strains share a nucleotide identity of 83% in the 5'NTR and 79.4% in the capsid coding region. The latter corresponds to 20 aa differences. Using a full length infectious clone of a cardiovirulent CB3 strain (B3/20) the 5'NTR and capsid proteins of the CO and AS strains were examined to determine their effect on cardiovirulence. Six chimeras were constructed in which 5'NTR and capsid sequences of B3/20 were replaced with the homologous sequences of AS or CO. Chimeric strains were tested for cardiovirulence phenotype by inoculation into C3H/HeJ mice. Hearts removed at 10 d post inoculation were examined for evidence of myocarditis by histophatology. When the B3/20 capsid coding region was replaced with the homologous region of AS or CO, the resultant chimeras produced widespread myocarditis similar to the parental B3/20; indicating that virulence determinant(s) did not exist in the capsid region. Chimeras containing the noncardiovirulent CO 5'NTR or CO 5'NTR+capsid failed to cause myocarditis; indicating that the CO 5'NTR conferred a noncardiovirulent phenotype. Chimeras containing the cardiovirulent AS 5'NTR alone or AS 5'NTR+capsid produced myocarditis; demonstrating that the AS 5'NTR conferred a cardiovirulent phenotype. These data provide evidence for the 5'NTR as the major determinant of myocarditic phenotype in naturally-occurring CB3. Studies are underway to identify 5'NTR cardiovirulence domains.