Human coronavirus (HCoV) strain 229E infection, but not HCoV strain OC43 infection, of monocytes/macrophages from healthy donors and patients with multiple sclerosis in remission resulted in increased apoptosis, as measured by DNA changes and annexin V staining. Apoptosis correlated with the differential release of infectious virus. HCoV strain 229E titers were 10(3.5) to 10(6) 50% tissue culture-infective doses (TCID(50))/ml, and HCoV strain OC43 titers were only 10(1.2) to 10(2.7) TCID(50)/ml.