Influence of complement on the neutralization of murine cytomegalovirus by rabbit antibody

Influenza virus-specific neutralizing IgM antibodies persist for a lifetime

Detection of immunoglobulin M (IgM) antibodies has long been used as an important diagnostic tool for identifying active viral infections, but their relevance in later stages has not been clearly defined in vivo. In this study, we followed the kinetics, longevity, and function of influenza virus-specific IgM antibodies for 2 years following sublethal infection of mice with live mouse-adapted A/PR/8/34 virus or immunization with formalin-inactivated virus. These groups mounted robust protective immune responses and survived lethal challenges with 50 × 50% lethal dose (LD50) mouse-adapted A/PR/8/34 virus 600 days after the primary exposure. Surprisingly, the virus-specific IgM antibodies persisted along with IgG antibodies, and we found a significantly higher number of IgM-positive (IgM(+)) virus-specific plasma cells than IgG(+) plasma cells that persisted for at least 9 months postexposure. The IgM antibodies were functional as they neutralized influenza virus in the presence of complement just as well as IgG antibodies did.

Detection of antibody to murine cytomegalovirus by enzyme-linked immunosorbent and indirect immunofluorescence assays

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.

Neutralization of different strains of murine cytomegalovirus (MCMV)-effect of in vitro passage

Two strains of mouse cytomegalovirus (MCMV) propagated in mouse salivary glands could be distinguished in neutralization tests. Cell (mouse embryo fibroblast)-passaged virus of either strain was generally 10-20 times easier to neutralize than virus produced in mouse salivary glands. Evidence was obtained that mouse immunoglobulin was attached to virus particles in salivary gland preparations. First, antibody to mouse immunoglobulin inactivated salivary gland virus but not cell culture-grown virus. Second, virus obtained from mice early after infection, before antibody production, was as easy to neutralize as cell culture-grown virus. The attached immunoglobulins were CMV-specific, non-neutralizing, and interfered with the action of neutralizing antibody. Non-neutralizing antibodies that bind to infectious virus particles are present in mouse serum at the time salivary glands are harvested, 3 weeks after infection.

Studies on the neutralization of herpes simplex virus. X. Demonstration of complement-requiring neutralizing (CRN) and slow-reacting CRN (s-CRN) antibodies in late IgG

A sample of late IgG from a rabbit hyperimmunized with herpes simplex virus was analyzed for neutralizing (N) and complement-requiring neutralizing (CRN) antibodies. In a usual endpoint test, N and CRN titers were 1: 40 and 1: 160, respectively, but when virus-IgG mixtures were incubated at 0 C overnight before addition of complement (C), an endpoint of 1:1280 was obtained. Virus sensitized at 0 C overnight required more C for inactivation than did sensitized virus formed earlier. Sensitization kinetic curve experiments employing a proper initial virus concentration, which permitted differentiation of sensitized viruses requiring different amounts of C, indicated that formation of sensitized virus detectable only with a relatively large amount of C proceeded slowly at IgG dilutions where the ordinary CRN antibody requiring a smaller amount of C was negligible. The results strongly suggested that the IgG sample contained slow-reacting CRN (s-CRN) antibody in excess of the hitherto known CRN antibody. As to the mechanism of formation of s-CRN complexes, experiments failed to prove the occurrence of complexes initially insensitive to C, and it appears more likely that s-CRN antibody has a comparatively low avidity for virus.

Characteristics of infection of B and T lymphocytes from mice after inoculation with cytomegalovirus

Viremia was produced by inoculating intravenously BALB/c mice with murine cytomegalovirus. Virus was detected in plasma and granulocytes only during the first 8 days after infection. Lymphocyte-associated viremia, detectable by cocultivation on syngeneic or allogeneic fibroblasts, persisted for at least 4 weeks. Eight to 10 days after infection, sonicated lymphocytes had no demonstrable free virus. When whole lymphocytes with no demonstrable free virus were enclosed in a Millipore chamber and placed on a fibroblastic feeder layer, T cells produced free virus but B cells did not. Compared to normal calf serum, specific hyperimmune serum reduced B cell-associated infectious centers by 74% and T cell-associated infectious centers by only 38%. Normal mouse sera reduced by 36% and 30% infectious center production by B cells and T cells, respectively. Lymphocytes enriched with Fc receptor-positive cells produced significantly more infectious centers than receptor-negative cells.

Antibody class and complement requirement of neutralizing antibodies in the primary and secondary antibody response of cattle to infectious bovine rhinotracheitis virus vaccine

Calves responded to a single intramuscular injection of an attenuated strain of infectious bovine rhinotracheitis virus by producing IgM followed by IgG antibody. Both IgM and IgG antibody produced during the first month were primarily complement-requiring neutralizing antibody (CRNAb), especially IgM antibody. After a month, IgG had replaced IgM as the predominant immunoglobulin, and titers with and without complement (C') decreased in both IgG and IgM fractions. The largest decrease was in the IgM CRNAb fraction. Seven days after a second injection given on day 196, calves responded with an anamnestic IgG response in which CRNAb titers were 1 or 2 two-fold dilutions higher than non-CRNAb titers. One calf developed an IgM response similar to its primary response, whereas inhibition of the IgM response occurred in the other 3 calves which had much lower IgM antibody titers than those attained in the primary response. Twenty-eight days after the second injection the titers of IgG were the same or only a 2-fold dilution less than their 7-day secondary titers, whereas IgM titers generally decreased considerably more than this. Guinea pig and rabbit sera were equally effective as C' sources in potentiating CRNAb, whereas bovine serum was a poor C' source.

Complement requirement of neutralizing antibodies in different classes of immunoglobulin appearing in rabbits and guinea pigs after primary and booster immunizations with herpes simplex virus

Rabbits and guinea pigs were immunized with herpes simplex virus and bled periodically. The sera were fractionated into slow IgG, fast IgG and IgM by DEAE-cellulose column chromatography, and complement-requiring (CRN) and nonrequiring neutralizing (N) antibody activities were estimated. In early sera of rabbits, the two IgG and IgM fractions possessed about equal CRN activities, although some animals showed a slightly lower activity in fast IgG. In guinea pigs, the early CRN activity resided mainly in slow IgS (7 S gamma2). The early IgG antibody of guinea pigs differed from that of rabbits in that it resembled IgM in resistances to heating at 70 C and to 2-merceptoethanol. The level of CRN IgM antibody in rabbits declined following a peak reached in 2 to 3 weeks, whereas such a decline was never observed in guinea pigs. N IgG antibody was developed a few weeks after the first immunization in rabbits and much retarded in guinea pigs. In both species, booster immunization quickly evoked N antibody in the two IgG fractions and also CRN IgM antibody, but in the case of rabbits the IgM antibody disappeared soon. It is concluded that IgG plays an important role in humoral immunity from the initial stage of the immunization course.

Comparative studies of the Smith and Raynaud strains of murine cytomegalovirus

A number of the biological, biophysical, and immunological parameters of the Smith and Raynaud strains of murine cytomegalovirus were compared. The two strains were found to be indistinguishable.