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. In the acute phase, IgG1 was seen first, followed by IgG2, IgG3, and IgG4 responses, the mean seropositivity of which gradually increased during convalescence, reaching 100% (standard deviation [SD], 84 to 100%), 57% (SD, 34 to 80%), 86% (SD, 66 to 100%), and 86% (SD, 66 to 100%), respectively. IgG2 rose and fell in connection with 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 acuteand 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 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 AND METHODSSerum specimens. A total of 154 positive human serum samples for measles antibodies were used in this study. Serum specimens were classified within two groups according to the characteristics of the measles cases from whic...
A total of 258 human sera positive for measles antibodies were divided into four different groups: group 1 contained 54 sera from children after natural measles infection (immunoglobulin M [IgM] positive, early infection phase), group 2 contained 28 sera from children after measles vaccination (IgM positive, early infection phase), group 3 contained 100 sera from healthy adults (natural long-lasting immunity), and group 4 contained 76 sera from healthy children (postvaccinal long-lasting immunity). In the early phase of infection, the percent distributions of measles virus-specific IgG isotypes were similar between natural and postvaccinal immune responses. IgG1 and IgG4 were the dominant isotypes, with mean levels of detection of 100% (natural infection) and 100% (postvaccinal) for IgG1 and 96% (natural infection) and 92% (postvaccinal) for IgG4. In comparison, the IgG4 geometric mean titer (GMT) in the early phase of natural infection was significantly higher than the IgG4 GMT detected in the postvaccinal immune response (80 versus 13; 95% confidence interval). In the memory phase, IgG2 and IgG3 responses decreased significantly in both natural infection and postvaccinal groups, while IgG1 levels were maintained. In contrast, the IgG4 postvaccinal immune response decreased strongly in the memory phase, whereas IgG4 natural long-lasting immunity remained unchanged (9 versus 86%; P < 0.05). The results obtained suggest that IgG4 isotype could be used in the early phase of infection as a quantitative marker and in long-lasting immunity as a qualitative marker to differentiate between natural and postvaccinal immune responses.
Hepatitis A, a vaccine preventable disease, is now of transitional or intermediate endemicity in Argentina, as the epidemiologic pattern of the disease has shifted with improvements in living conditions in some parts of the country. Increase in the susceptibility of older children and adults has led to increasing disease incidence. Molecular epidemiology has played an important role in the understanding of HAV infection by identifying modes of spreading and by permitting the monitoring of changes in circulating virus brought about by prevention programs. South American isolates characterized are limited. Eighty-two sporadic and outbreak isolates from Argentina were sequenced in the VP1/2A region of HAV genome over a 9-year period. All the isolates belonged to subgenotype IA. All our sequences grouped into two big clusters. Apparently, at least two lineages have been co-circulating in the same place at the same time. Despite great genetic variability, few point amino acid changes could be deduced. Four sequences showed an Arg --> Lys substitution at 1-297 which characterized the genotype IB at the amino acid level. Many isolates carried a conservative amino acid substitution Leu --> Ile at position 42 of the 2A domain, previously described as a possible fingerprint of HAV sequences in Brazil. The other rare changes have been found before, except for a 1-277 Asn --> Ser substitution displayed in two isolates that has not been previously reported. Argentina recently implemented universal vaccination in 1-year-old children. Molecular tools would be useful in an active surveillance program.
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