We have compared murine cytomegalovirus (MCMV) antibody determination by enzyme-linked immunosorbent assay (ELISA) and indirect immunofluorescence assay. A comparison of antibody detection with 146 serum samples at a 1:20 dilution showed 100% agreement (60 negatives and 86 positives) between the assays. There was close agreement of endpoint determinations of sera by both methods. After experimental MCMV infection, antibody to MCMV was detected by both assays as early as day 7, and high titers persisted as late as 6 months. In contrast to immunocompetent littermates, athymic nude mice did not develop antibody after infection. Mice lacking antibody detectable by ELISA were susceptible to lethal MCMV challenge. In a survey of animals from five commercial sources, MCMV antibody was not detected unless mice were experimentally infected. MCMV antibody determination by ELISA is a convenient method, comparable to the indirect immunofluorescence assay in sensitivity and specificity. * Corresponding author. response to MCMV infection and to determine the frequency of preexisting antibody in uninfected mice supplied by commercial sources. MATERIALS AND METHODS Mice. For these experiments, male and female BALB/c AnN, female DBA/2N, and homozygous (nu/nu) and heterozygous (nul+) athymic nude mice were obtained from Charles River Breeding Laboratories, Inc., Kingston, N.Y. C57BLk/1OSCN and BlO.A mice were obtained from Harlan Sprague-Dawley Inc., Madison, Wis. BALB/c heterozygous and homozygous nude mice were obtained from the National Cancer Institute, Frederick, Md. Female BlO.BR and C57BL/1OSNJ (B10) mice were purchased from Jackson Laboratory, Bar Harbor, Maine. In addition, male and female BALB/c AnN and BlO.BR mice were bred in our animal care facility. Animals were maintained in groups of 5 to 10 in isolator units and were fed Laboratory Chow 500 (Ralston Purina, St. Louis, Mo.) and water ad libitum. The colony was monitored for both MCMV infection and other respiratory pathogens. The mice were 6 to 8 weeks of age before use. Virus. The Smith strain of MCMV was originally obtained from M. C. Jordan, University of Minnesota, Minneapolis. The virus was maintained by serial passage in BALB/c mice and was prepared as a 10% (wt/vol) homogenate of salivary gland tissue. The inoculum for sham-infected controls was prepared from the salivary glands of uninfected BALB/c mice. Virus and control stocks were stored at-70°C with 10% dimethyl sulfoxide as a stabilizer. The virus pool for these experiments, which contained 1.6 x 107 PFU of virus per ml, was screened by an antibody generation test (Microbiological Associates, Bethesda, Md.) and was found to be free of other murine pathogens, including pneumonia virus of mice, reovirus type 3, K virus, polyomavirus, Sendai virus, minute virus of mice, murine adenovirus, lymphocytic 600
