The antigen-limited nature of microtiter ELISAs requires partial depletion of IgG to permit reliable determination of rabbit serum IgA antibody activity

Comparative immunogenicity in mice of rotavirus VP6 tubular structures and virus-like particles

Rotavirus (RV) is the most important cause of severe gastroenteritis in children worldwide. Current live RV vaccines are efficacious but show lower efficacy in developing countries, as well as a low risk of intussusception. This has led to the development of parenteral non-live candidate vaccines against RV. RV capsid VP6 protein is highly conserved and the most abundant RV protein forming highly immunogenic oligomeric structures with multivalent antigen expression. Both recombinant VP6 (rVP6) or double-layered (dl) 2/6-virus-like particles (VLPs), might be considered as the simplest RV subunit vaccine candidates. Human rVP6 protein and dl2/6-VLPs were produced in Sf9 insect cells by baculovirus expression system. Formation of rVP6 tubules and VLPs were confirmed by electron microscopy. BALB/c mice were immunized intramuscularly, and immune responses were analyzed. Both rVP6 and dl2/6-VLPs induced a balanced Th1-type and Th2-type response and high levels of serum IgG antibodies with cross-reactivity against different RV strains (Wa, SC2, BrB, 69M, L26, WC3, and RRV). In addition, mucosal VP6-specific IgG and IgA antibodies were detected in feces and vaginal washes (VW) of immunized animals. Importantly, VWs of immunized mice inhibited RV Wa and RRV infection in vitro. Immunization with either protein preparation induced a similar level of VP6-specific, interferon-γ secreting CD4(+) T cells in response to different RVs or the 18-mer peptide (AA 242-259), a VP6-specific CD4(+) T cell epitope. RV rVP6 and dl2/6-VLPs induced equally strong humoral and cellular responses against RV in mice and therefore, may be considered as non-live vaccine candidates against RV.

IgA antibody response of swine to foot-and-mouth disease virus infection and vaccination

Foot-and-mouth disease virus (FMDV) continues to be a significant economic problem worldwide. Control of the disease involves the use of killed-virus vaccines, a control measure developed decades ago. After natural infection, the primary site of replication of FMDV is the pharyngeal area, suggesting that a mucosal immune response is the most effective. Humoral immunity to killed-virus vaccination induces antibodies that can prevent the clinical disease but not local infection. Determining whether infection or vaccination stimulates IgA-mediated local immunity depends on the method of analysis. Different assays have been described to analyze the quality of antibody responses of cattle and swine to FMDV, including indirect double-antibody sandwich enzyme-linked immunosorbent assay (IDAS-ELISA) and antibody capture assay-ELISA (ACA-ELISA). We tested these assays on swine and show that vaccinated animals had FMDV-specific IgM and IgG but no IgA in either serum or saliva. After the infection, both assays detected FMDV-specific IgM, IgG, and IgA in serum. Notably, serum IgA was more readily detected using the ACA-ELISA, whereas IgA was not detected in saliva with this assay. FMDV-specific IgA antibodies were detected in saliva samples using the IDAS-ELISA. These data show that parenterally administered, killed-virus vaccine does not induce a mucosal antibody response to FMDV and illuminates limitations and appropriate applications of the two ELISAs used to measure FMDV-specific responses. Further, the presence of the IgA antivirus in serum correlates with the presence of such antibodies in saliva.

Passive adsorption of immunologically active and inactive synthetic peptides to polystyrene is influenced by the proportion of non-polar residues in the peptide

A well-known drawback in the use of synthetic peptides as solid-phase antigens in immunoassays is that positive controls confirming the presence of the peptide on the solid phase are not always present. We therefore evaluated the applicability of a recently described enzyme immunoassay (EIA) method by which the presence of peptides is detected by biotinylation (BioEIA) of alpha- and/or epsilon-amino groups after passive adsorption. This approach allows the rapid screening of a large number of proteins and peptides in respect to passive adsorption to plastic surfaces. When using irradiated polystyrene microplates we found that 240 (94%) of 256 synthetic peptides, covering 85% of the complete hepatitis C virus (HCV) sequence, passively adsorbed to polystyrene. When comparing the results from the BioEIA to the peptide reactivity of human sera it was obvious that the absence of serum reactivities was not due to lack of peptide adsorption to the plates. Using 192 peptides the relation between the signal-to-cutoff ratio (S/CO) in the BioEIA and the amino acid content of the individual peptides was further analyzed. The S/CO ratio was related to the number of epsilon NH2 groups (Lys residues) present in the peptide (P < 0.001, Kruskal-Wallis). We separately related the amino acid content of 68 peptides with Lys and 124 peptides lacking Lys to the S/CO ratio in the BioEIA. In both cases it was found that an increasing amount of nonpolar residues such as Ala, Phe, Ile, Met, and Val (P < 0.05, respectively) in the peptides was related to a lower S/CO ratio in the BioEIA.(ABSTRACT TRUNCATED AT 250 WORDS)

Interference of immunoglobulin G (IgG) antibodies in IgA antibody determinations of Chlamydia pneumoniae by microimmunofluorescence test

In the microimmunofluorescence test for measuring immunoglobulin A (IgA) antibodies against Chlamydia pneumoniae, removal of interfering IgG antibodies made IgA antibody reactivity patterns in 952 serum samples easier to interpret, prozone effects disappeared, and titers increased, especially in the sera with high IgG titers. IgA rheumatoid factors did not interfere in the assay.

Characterization of the pseudorabies virus-specific immunoglobulin M response and evaluation of its diagnostic use in pigs with preexisting immunity to the virus

Despite preexisting immunity to pseudorabies virus (PRV), pigs may become infected and may or may not show clinical signs of disease. To investigate whether detection of immunoglobulin M (IgM) antibodies to PRV is suitable for diagnosis of recent infection in pigs with (or without) preexisting immunity, the IgM responses of pigs were examined after both experimental and natural infections. Upon inoculation of seronegative pigs with a low dose of a mildly virulent strain of PRV, IgM was first detectable at day 7 postinoculation (p.i.), reached a maximum at day 14 p.i., and became undetectable again at about days 32 to 36 p.i. In inoculated pigs with maternal antibodies against PRV, the IgM response began later and ended sooner, and peak titers were also lower. In immune pigs with maternally derived antibodies, there was apparently no correlation between the virulence of the inoculated strain and the IgM response. The suitability of the IgM enzyme-linked immunosorbent assay (ELISA) for detection of recent infection in the field was compared with that of the virus neutralization (VN) assay and with an ELISA which specifically detects antibodies directed to glycoprotein I (gI) of PRV. Paired sera were obtained from pigs suspected of PRV infection in an area endemic for PRV infection in which vaccination against PRV is often applied. Practically all pigs had antibodies to PRV in the acute phase of the disease. Compared with the VN assay, the specificity of the IgM ELISA was high but its sensitivity was low. However, all three serotests apparently failed to detect some PRV infections. The IgM ELISA appeared to be especially useful as a diagnostic aid for detection of recent infections in pigs with high levels of neutralizing and gI antibodies, probably maternally derived, in the acute phase of the disease. Such pigs may fail to develop a significant rise in VN antibody titer. The IgM ELISA may be the only serotest for monitoring infections in such pigs.

Measurement of isotype-specific antibody responses to Aujeszky's disease virus in sera and mucosal secretions of pigs

Enzyme-linked immunosorbent assays (ELISAs) for the detection of porcine IgM, IgA, IgG1 and IgG2 antibodies directed against Aujeszky's disease virus (ADV) are described. ADV-specific IgA and IgM were detected in an antibody capture assay, and ADV-specific IgG1 and IgG2 were detected in an indirect double antibody sandwich assay. A selected set of samples was tested in the four ELISAs and in a 24 h virus neutralization assay. Comparison of the results showed that the ELISAs were isotype-specific, sensitive, and reproducible. Samples with ADV antibody of one isotype showed that ADV-specific IgG1, IgG2 and IgM were able to neutralize the virus in vitro. In vitro neutralization of virus can be enhanced by complement. ADV-specific IgA neutralized virus only weakly. ADV-infected cells activated complement in the absence of antibody. Specific IgG2 and IgM enhanced complement activation. Analysis of the time course of antibody responses after infection or vaccination revealed that the isotype-specific ELISAs are suitable to study the humoral antibody response of pigs to the virus in mucosal secretions. Wild-type virus (strain NIA-3) and an attenuated vaccine strain (Bartha) administered intranasally induced mucosal IgM and IgA responses to the virus. In contrast, a killed vaccine (Nobivac) administered intramuscularly induced only weak mucosal IgM responses. The attenuated vaccine strain primed for a mucosal IgA memory response evoked upon challenge infection with wild-type virus.