PERSISTENCE OF REPLICATING COXSACKIEVIRUS B3 IN THE ATHYMIC MURINE HEART IS ASSOCIATED WITH DEVELOPMENT OF MYOCARDITIC LESIONS

Coxsackievirus B3 (CVB3)-induced myocarditis was studied in euthymic ( nu/+) and athymic (nu/nu) C3H/HeN (H-2(k)) mice. Mice were inoculated intraperitoneally with 10(6) p.f.u. of CVB3 (Nancy strain) and sacrifi ced at intervals up to 92 days post-inoculation (p.i.). Viraemia peake d at day 2 to 3 p.i. and ceased at day 5 to 7 p.i. in a synchronized m anner in both sets of mice. Very few infectious particles were detecte d in the blood of nu/nu mice after day 14 p.i. In nu/nu mice, CVB3 per sisted in myocardial tissue with constant titres between 2.7 +/- 1.9 x 10(4) and 7.6 +/- 5.2 x 10(4) p.f.u./mg from day 3 to 92 p.i., which were comparable to those of nu/+ mice in the acute phase. In nu/+ mice , the virus was recovered from all animals examined by day 11 p.i. and from three out of 13 mice between days 14 and 21 p.i., yet no virus w as recovered from nu/+ mice at day 42 p.i. In nu/nu mice, sense and an tisense RNA for CVB3 was detected in the myocardial tissue up to day 4 2 p.i. by in situ hybridization and up to day 92 p.i. by reverse trans criptase-PCR. Neither sense nor antisense RNA was detected after day 2 1 p.i. in nu/+ mice with the same techniques. Myocardial tissue damage was analysed morphologically. At day 92 p.i., the area of myocardial injury peaked at 23 % of the section in nu/nu mice. In contrast, less than 0.6% of tissue sections contained lesions in nu/+ mice. A neutral izing antibody response to CVB3 was observed in both nu/nu and nu/+ mi ce. The mean titre of neutralizing antibody was significantly higher a t day 21 p.i. in nu/+ mice, but similar at day 42 p.i. with nu/nu and nu/+ mice. Perforin-producing natural killer-like cells, which are con sidered to play an important role in causing acute myocarditic lesions in immunocompetent mice, were found in the lesions of nu/nu mice pers istently infected with CVB3. Prolonged tumour necrosis factor-alpha mR NA synthesis detected in nu/nu mice appears to reflect the continuous activation of macrophages, which extend phagocytic reactions to virus- infected myocytes. These immunological results suggested that the host immune response devoid of antigen-specific T cell function is not suf ficient to terminate CVB3 infection in nu/nu mice. Also, it appears th at competent cellular immunity, on the whole, plays a role in curing r ather than in aggravating myocarditis in nu/+ mice. In conclusion, our results indicate that the presence of replicating CVB3 is an importan t factor in the development of myocarditic lesions in C3H/HeN mice.