A total of 154 human serum samples (32 acute-phase and 22 convalescent-phase serum samples obtained within a week and between days 8 and 26 after the onset of rash, respectively, and 100 samples drawn from healthy immune adults) were processed by an immunofluorescence assay for the detection of immunoglobulin M (IgM), total immunoglobulin G (IgG), IgG1, IgG2, IgG3, and IgG4 measles virus-specific antibodies. detection of IgG2 and/or IgG3 subclass antibodies of 95.5% (range, 100 to 86.5%) in the convalescent phase of infection. The mean percentage of measles IgG2 and IgG3 seropositivity dropped significantly during the memory phase, to 2% (range, 2 to 6%) and 3% (range, 3 to 7%), respectively (< 0.05); meanwhile IgG1 and IgG4 subclass responses remained relatively unmodified in samples obtained years after infection (mean 100% [SD, 96 to 100%] and 86% [SD, 79 to 93%], respectively). Results obtained defined two highly different immune isotypic response patterns. One Rabbit Polyclonal to Doublecortin (phospho-Ser376). pattern is restrictive to IgG2 and/or IgG3 in the convalescent phase and is kinetically similar to the IgM antibody response, so its detection could be referred to as a recent viral activity. On the other hand, IgG1 and IgG4 were detected in both the convalescent and memory phases of the immune response, but their isolated occurrence without IgG2 and IgG3 could be related to the long-lasting immunity. Measles has been targeted for global eradication by the World Health Organization’s Expanded Programme on Immunization; for the effective control and eventual eradication of measles, it is necessary to impair measles transmission by establishing herd immunity. To accomplish this aim, a sensitive surveillance system is essential to detect wild-virus circulation, as well as sensitive and specific diagnostic tests (4, 5). The diagnosis of measles infection is serologically confirmed by the presence of a fourfold rise in antibody titers for paired acute- and convalescent-phase sera or most often by detection of anti-measles virus immunoglobulin M (IgM) antibody. The performance of IgM detection for the differentiation of primary and secondary measles antibody responses depends upon (i) propagation of the virus within the community, (ii) characteristics of the individual immune response, (iii) time of specimen collection, and (iv) assay sensitivity. Similar to other serological markers, a subclass-restricted response to antigens has been recently demonstrated (8, 9, 10, 12, 18); however, a limited amount of data is available on the virus-specific immunoglobulin G (IgG) subclass responses during the ordinary course of measles viral infection. Narita et al. suggested that the IgG3 response could play a major role in acute-phase immunity during primary infection, while the IgG1 response could be related to maintenance of measles immunity (14). These data offer Pracinostat early support for the hypothesis that the IgG isotypic immune response could also be a useful serologic tool, in addition to specific measles IgM antibody detection, to eventually distinguish between early and late measles infection. The present study was undertaken to point out the specific antiviral IgG1, IgG2, IgG3, and IgG4 subclass response patterns elicited during natural infection (acute and convalescent phases) as well as in the long-lasting humoral immunity to measles virus. The aim of this paper is to contribute to the global understanding of antibody responses to measles virus infections. MATERIALS Pracinostat AND METHODS Serum specimens. A total of 154 positive human serum samples for measles antibodies Pracinostat were used in this study. Serum specimens were classified within two groups according to the characteristics of the measles cases from which they were obtained. In group 1 were 54 serum samples collected during a measles virus outbreak in Argentina in 1998. 32 of these were acute serum samples obtained within a week after the onset of rash (median, 3 days; range, 1 to 7 days) and 22 were convalescent serum samples obtained between days 8 and 26 (median, 17 days) after the onset of rash. The diagnosis was confirmed by the detection of measles-specific IgM antibodies by immunofluorescence assay (IFA) test as a screening method, and it was subsequently ratified by capture enzyme immunoassays (6, 17). In group 2 were 100 serum samples obtained from healthy adults with detectable neutralizing measles antibodies who reported a history of natural, long-past measles infection that occurred at least 10 years earlier. Antisera. Mouse monoclonal antibodies to human IgG subclasses were obtained from Sigma Chemical Co., St. Louis, Mo. These antibodies were used at dilutions of 1 1:100 (IgG1), 1:32 (IgG2), 1:32 (IgG3), and 1:32 (IgG4) according to the manufacturer’s instructions. Rabbit monoclonal antibodies to human IgM and total IgG were obtained from CAPPEL and used at dilutions of 1 1:100 and 1:150, respectively. The optimal dilutions of monoclonal antibodies were determined by titrations against reference positive sera diluted 1:20 (initial dilution of serum for IFA assay). Preparation of antigen slides. A suspension of Vero cells (105 cells/ml) was seeded onto.