Protective local and systemic antibody responses of swine exposed to an aerosol of Actinobacillus pleuropneumoniae serotype 1.

The isotype-specific antibody responses in serum and in nasal and pulmonary lavage fluids of swine following aerosol immunization with an attenuated strain of Actinobacillus pleuropneumoniae serotype 1, strain CM5A, was investigated. The presence of immunoglobulin G (IgG), IgA, and IgM with specificities for capsular polysaccharide, lipopolysaccharide, and hemolysin was determined by enzyme-linked immunosorbent assay by using purified antigens. Strain CM5A induced serum antibodies of each isotype to the three antigens. The serum antibody response was sustained and typical of persistent antigenic stimulation. The specific IgM response decreased and the specific IgG response increased after challenge with strain CM5. IgA specific for the three antigens was detected in nasal secretions from all immune pigs, whereas specific IgG could only be detected in samples contaminated with blood. Both IgA and IgG specific for each of the antigens were detected in pulmonary lavage samples. There was no significant increase in specific IgA in nasal secretions; however, levels of lipopolysaccharide-specific and hemolysin-specific IgG and IgA in pulmonary secretions rose after aerosol challenge with strain CM5. Passive transfer of immune swine serum resulted in protection against pleuropneumonia and in levels of specific serum IgG which were similar to those in actively immunized pigs. It is concluded that specific serum IgG antibodies are important in protection from porcine pleuropneumonia.     

Immunoglobulin A-deficient mice exhibit altered T helper 1-type immune responses but retain mucosal immunity to influenza virus

We have previously demonstrated that immunoglobulin A (IgA)(-/-) knockout (KO) mice exhibit levels of susceptibility to influenza virus infection that are similar to those of their normal IgA(+/+) littermates. To understand the mechanism of this apparent mucosal immunity without IgA, immunoglobulin isotype and T helper 1 (Th1)-type [interferon-gamma (IFN-gamma)] and Th2-type [interleukin (IL)-4, IL-5)] cytokine responses to influenza vaccine were evaluated. Intranasal immunization with influenza virus subunit vaccine plus cholera toxin/cholera toxin B subunit (CT/CTB) induced significant influenza virus-specific immunoglobulin G (IgG) antibody in the serum and nasal passages of both IgA(-/-) and IgA(+/+) mice, while IgA antibodies were induced only in IgA(+/+) mice. IgA KO mice exhibited an IgG1 subclass haemagglutinin (HA)-specific response but no detectable IgG2a and IgG2b responses. In contrast, IgA(+/+) mice exhibited significant IgG1 as well as IgG2a responses. This indicates a predominant Th2-type response in IgA KO mice compared to normal mice. Following stimulation with influenza virus in vitro, splenic lymphocytes from immunized IgA(-/-) mice produced significantly lower levels of IFN-gamma than IgA(+/+) mice (P < 0.001), but elaborated similar levels of IL-4 and IL-5. This was true at both protein and mRNA levels. Immunized mice were challenged intranasally with a small inoculum of influenza virus to allow deposition of virus in the nasal mucosal passages. Compared to non-immunized mice, immunized IgA(-/-) and IgA(+/+) mice exhibited significant, but similar levels of reduction in virus titres in the nose and lung. These results demonstrate that in addition to IgA deficiency, IgA gene deletion also resulted in down-regulated Th1-type immune responses and confirm our previous data that IgA antibody is not indispensable for the prevention of influenza virus infection.     

The susceptibility of breast-fed and cow's milk formula-fed infant guinea pigs to upper respiratory tract infection with influenza virus

Breast-fed infant guinea pigs from immune mothers were partially protected against infection with influenza virus when compared to those from nonimmune mothers. Virus titres in nasal washes at 24 h post-infection were reduced and virus clearance from the upper respiratory tract accelerated. When infants of immune mothers were deprived of colostrum and hand-reared on a formula-feed their ability to reduce virus yields at 24 h post-infection was lost. Infants partially breast-fed and partially formula-fed gave total virus yields similar to their fully breast-fed peers. Infants of immune mothers possessed high titres of serum IgG antibody to the virus prior to infection. Post-infection, IgG antibodies appeared on the mucosal surface of breast-fed seropositive infants earlier than for seronegative infants of nonimmune mothers but IgM and IgA responses of seropositive infants were less vigorous than those of seronegative infants. There was little evidence that antibody present in a mother's milk was transmitted to the nasal mucosa of her offspring. Fully and partly formula-fed seropositive infants showed enhanced transudation of serum IgG antibody on to the mucosal surface and this effect was most marked in the partly formula-fed group which showed greater protection. In both formula-fed groups serum and nasal IgM and IgA responses were completely suppressed.     

The susceptibility of breast-fed and cow's milk formula-fed infant guinea pigs to upper respiratory tract infection with influenza virus.

Breast-fed infant guinea pigs from immune mothers were partially protected against infection with influenza virus when compared to those from nonimmune mothers. Virus titres in nasal washes at 24 h post-infection were reduced and virus clearance from the upper respiratory tract accelerated. When infants of immune mothers were deprived of colostrum and hand-reared on a formula-feed their ability to reduce virus yields at 24 h post-infection was lost. Infants partially breast-fed and partially formula-fed gave total virus yields similar to their fully breast-fed peers. Infants of immune mothers possessed high titres of serum IgG antibody to the virus prior to infection. Post-infection, IgG antibodies appeared on the mucosal surface of breast-fed seropositive infants earlier than for seronegative infants of nonimmune mothers but IgM and IgA responses of seropositive infants were less vigorous than those of seronegative infants. There was little evidence that antibody present in a mother''s milk was transmitted to the nasal mucosa of her offspring. Fully and partly formula-fed seropositive infants showed enhanced transudation of serum IgG antibody on to the mucosal surface and this effect was most marked in the partly formula-fed group which showed greater protection. In both formula-fed groups serum and nasal IgM and IgA responses were completely suppressed.     

Topical application of human-derived Ig isotypes for the control of acute respiratory infection evaluated in a human CD89-expressing mouse model

Recurrent and persistent airway infections remain prevalent in patients with primary immunodeficiency (PID), despite restoration of serum immunoglobulin levels by intravenous or subcutaneous plasma-derived IgG. We investigated the effectiveness of different human Ig isotype preparations to protect mice against influenza when delivered directly to the respiratory mucosa. Four polyvalent Ig preparations from pooled plasma were compared: IgG, monomeric IgA (mIgA), polymeric IgA-containing IgM (IgAM) and IgAM associated with the secretory component (SIgAM). To evaluate these preparations, a transgenic mouse expressing human FcαRI/CD89 within the myeloid lineage was created. CD89 was expressed on all myeloid cells in the lung and blood except eosinophils, reflecting human CD89 expression. Intranasal administration of IgA-containing preparations was less effective than IgG in reducing pulmonary viral titres after infection of mice with A/California/7/09 (Cal7) or the antigenically distant A/Puerto Rico/8/34 (PR8) viruses. However, IgA reduced weight loss and inflammatory mediator expression. Both IgG and IgA protected mice from a lethal dose of PR8 virus and for mIgA, this effect was partially CD89 dependent. Our data support the beneficial effect of topically applied Ig purified from pooled human plasma for controlling circulating and non-circulating influenza virus infections. This may be important for reducing morbidity in PID patients.     

Monoclonal antibodies against bovine immunoglobulins and their use in isotype-specific ELISAs for rotavirus antibody

Monoclonal antibodies (MCA) against bovine immunoglobulin (BIg) isotypes were produced and characterized. MCAs were obtained which react specifically with IgG, IgG1, IgG2 or IgA while MCAs against IgM showed a partial cross-reaction with affinity purified IgA. MCAs with optimal characteristics for application in ELISA were selected and used as conjugates in an indirect double antibody sandwich assay (IDAS) and as the capturing antibody in an antibody capture assay (ACA) for the isotype-specific detection of antibodies against rotavirus. Based on theoretical grounds, experimental analysis of inter- and intra-isotype competition in IDAS and ACA, respectively, and a direct comparison of both tests, the IDAS was selected for the detection of IgG1 and IgG2 anti-rotavirus antibodies. The ACA was the test of choice for the detection of IgM and IgA anti-rotavirus antibodies. The isotype specificity of these tests relies on the specificity of the MCAs and was confirmed for each test by the observation that samples containing rotavirus antibodies of only 1 particular isotype reacted only in the homologous assay. The MCAs against bovine Ig isotypes and isotype-specific ELISAs were found to be very useful in the study of humoral mucosal immunity in calves infected with rotavirus.     

Secretory IgA antibodies provide cross-protection against infection with different strains of influenza B virus

This study examined whether secretory IgA (S-IgA) antibodies (Abs) could confer cross-protective immunity against infection with influenza B viruses of antigenically distinct lineages. Wild-type or polymeric Ig receptor (pIgR)-knockout (KO) mice were immunized by infection with different B viruses or by intranasal (i.n.) administration with different inactivated vaccines. Four weeks later mice were challenged with either the B/Ibaraki/2/85 virus, representative of the B/Victoria/2/87 (B/Victoria)-lineage, or B/Yamagata/16/88 virus, representative of the B/Yamagata-lineage. Three days after challenge, nasal wash and serum specimens were assayed for IgA and IgG Abs specific for challenge viral antigens and for protection against challenge viruses. In wild-type mice, B/Ibaraki (or B/Yamagata) cross-reactive IgA Abs were detected at higher levels when infected or immunized with homologous-lineage viruses and at lower levels when infected or immunized with heterologous-lineage viruses. There was a correlation between the amount of nasal cross-reactive IgA Ab and the efficacy of cross-protection with a homologous-lineage virus. In mice lacking the pIgR, nasal cross-protective IgA Abs were only marginally detected in vaccinated mice and an accumulation of IgA in the serum was observed. This reduction of nasal IgA was accompanied by inefficient cross-protection against the B/Ibaraki (or B/Yamagata) virus infection. These results suggest that challenge viral-antigen cross-reactive S-IgA in nasal secretions induced by i.n. infection or vaccination is involved in providing cross-protection against challenge infection with virus within either the B/Victoria- or B/Yamagata-lineage.     

Indirect double sandwich ELISA for the specific and quantitative measurement of mouse IgM, IgA and IgG subclasses

We have developed sensitive enzyme-linked immunosorbent assays (ELISA) which measure mouse serum heavy chain immunoglobulin isotypes in nanograms per milliliter. In each case the specific isotypic Ig is sandwiched between an isotype-specific antibody used for coating and another isotype-specific antibody coupled to biotin for detection (with alkaline phosphatase coupled to avidin). These methods are simple to perform, specific for each isotype, reproducible with an average coefficient of variation of 5% for IgG1, 3% for IgG2a, 7% for IgG2b, 10% for IgG3, 3% for IgA and 7% for IgM, and at least 100 times more sensitive than radial immunodiffusion. The assays have been used to determine the absolute concentrations of mouse serum heavy chain Ig isotypes.     

Immunoglobulin M and G antibody response to type- and subtype-specific antigens after primary and secondary exposures of mice to influenza A viruses.

A mouse model of influenza infection was studied to help define parameters that may affect serodiagnosis of human infections by immunoassays. Antibodies to both type- and subtype-specific influenza A antigens were measured by a solid-phase immunofluorometric assay. Dilute mouse sera were added to purified influenza virus that had been covalently bound to polyaminostyrene microbeads, and the bound antibody was detected by fluorescein isothiocyanate-labeled isotype-specific antisera. Results were consistent in that upon exposure of mice by either infection alone or by vaccination after infection, both immunoglobulin M (IgM) and IgG antibodies reactive with newly encountered subtype specific viral antigens were measured. IgG antibody was usually detectable by the solid-phase immunofluorometric assay several days before it could be detected by a hemagglutination inhibition test. Increased levels of antibody of the IgG1, IgGa, IgG2b, and IgG3 subclasses were also measured during influenza infection. Surprisingly, response to type-specific viral antigens was of the IgG class in primary as well as in secondary exposure. The results suggest that for serodiagnosis of influenza infections by detection of specific IgM antibody, the assay should use subtype-specific antigens.     

Tracheal and bronchial polymeric immunoglobulin secretory immune system (PISIS) development in a porcine model

Polymeric immunoglobulins (pIgs) mucosal secretion is mediated by the pIg secretory immune system (PISIS), which is composed of J-chain (JC) and antibody (IgM/IgA) producing cells (JC-AbPC), pIg receptor (pIgR) epithelial cell expression and the efficient release of secretory Igs (SIgs) to the mucosal lumen. A poor development or disturbances in this system may cause higher infection susceptibility, as observed in young and elderly people. In spite of this system's importance, few detailed studies regarding its development have been described in the lower respiratory tract of humans. Because the porcine model has been reported as an option for translational medicine to humans, we studied the tracheal and bronchial PISIS development in healthy, non-vaccinated, SPF, miniature Vietnamese pigs from birth to adulthood using immunohistochemistry and ELISAs. Our results demonstrated that pIgR was present at birth, and its expression increased with age. In contrast, JC-AbPC were low in neonatal pigs; however, colostrum was a source of IgM, SIgA, total IgA and IgG in respiratory secretions (trachea and bronchoalveolar lavages, nasal secretion and saliva) in piglets. JC-AbPC steadily increased in post-weaned, young and adult pigs, correlating with considerable increases in secretory and total Igs in the trachea and bronchi. These data suggest a compensatory role of maternal Igs at the respiratory mucosa in the absence of a structured PISIS before weaning. Furthermore, monomeric Igs (IgG and IgA) may also play an important role in respiratory protection and deserves a more thorough study.     

Protection against influenza virus infection by intranasal vaccine with surf clam microparticles (SMP) as an adjuvant

A safe and effective adjuvant is necessary to enhance mucosal immune responses for the development of an inactivated intranasal influenza vaccine. The present study demonstrated the effectiveness of surf clam microparticles (SMP) derived from natural surf clams as an adjuvant for an intranasal influenza vaccine. The adjuvant effect of SMP was examined when co-administered intranasally with inactivated A/PR8 (H1N1) influenza virus hemagglutinin vaccine in BALB/c mice. Administration of the vaccine with SMP induced a high anti-PR8 haemagglutinin (HA)-specific immunoglobulin A (IgA) response in the nasal wash and immunoglobulin G (IgG) response in the serum, resulting in protection against both nasal-restricted infection and lethal lung infection by A/PR8 virus. In addition, administration of SMP with A/Yamagata (H1N1), A/Beijing (H1N1), or A/Guizhou (H3N2) vaccine conferred complete protection against A/PR8 virus challenge in the nasal infection model, suggesting that SMP adjuvanted vaccine can confer cross-protection against variant influenza viruses. The use of SMP is suggested as a new safe and effective mucosal adjuvant for nasal vaccination against influenza virus infection.     

Quantification and origin of the immunoglobulins in porcine respiratory tract secretions.

The immunoglobulin content of porcine nasal, tracheal and bronchio-alveolar secretions was determined. IgA was the predominant immunoglobulin in nasal and tracheal secretions, there being no significant difference (P greater than 0.01) between their IgA:IgG ratios of 2.7:1 and 2.4:1, respectively. In contrast, IgG was the predominant immunoglobulin in bronchioalveolar secretions, the IgA:IgG ratio being 0.7:1. The ability of tracheal and lung tissue to synthesize IgA and IgG was determined in vitro. Tracheal cultures synthesized more IgA than IgG whereas in the lungs the reverse occurred, the ratio of IgA:IgG synthesis being 1.4:1 and 0.4:1, respectively. The proportion of serum-derived IgA and IgG in respiratory tract secretions was determined by measuring the transfer of 125I- and 131I-labelled immunoglobulins from serum. It appeared that more than 97% of the IgA was produced locally. More significantly a proportion of the IgG was also synthesized locally. This proportion was smallest in nasal secretions (21.8%) and greatest in bronchio-alveolar secretions (62.6%). The results suggest that IgG, a large proportion of which is locally synthesized, is important in the homeostatic mechanisms of the lower respiratory tract.     

Use of Recombinant Nucleoproteins in Enzyme-Linked Immunosorbent Assays for Detection of Virus-Specific Immunoglobulin A (IgA) and IgG Antibodies in Influenza Virus A- or B-Infected Patients

The nucleoprotein genes of influenza virus A/Netherlands/018/94 (H3N2) and influenza virus B/Harbin/7/94 were cloned into the bacterial expression vector pMalC to yield highly purified recombinant influenza virus A and B nucleoproteins. With these recombinant influenza nucleoproteins, enzyme-linked immunosorbent assays (ELISAs) were developed for the detection of influenza virus A- and B-specific immunoglobulin A (IgA) and IgG serum antibodies. Serum samples were collected at consecutive time points after the onset of clinical symptoms from patients with confirmed influenza virus A or B infections. Nucleoprotein-specific IgA antibodies were detected in 41.2% of influenza virus A-infected patients and in 66.7% of influenza virus B-infected patients on day 6 after the onset of clinical symptoms. In serum samples taken on day 21 (influenza virus A-infected patients) or day 28 (influenza virus B-infected patients), nucleoprotein-specific IgA antibodies could be detected in 58.8 and 58.3% of influenza virus A- and B-infected patients, respectively. At the same time, IgG antibody rises were detected in 88.2% of influenza virus A-infected patients and in 95.8% of influenza virus B-infected patients. On comparison, hemagglutination inhibition assays detected antibody titer rises in 81.3 and 72.7% of patients infected with influenza viruses A and B, respectively. In contrast to the detection of nucleoprotein-specific IgG antibodies or hemagglutination-inhibiting antibodies, the detection of nucleoprotein-specific IgA antibodies does not require paired serum samples and therefore can be considered an attractive alternative for the rapid serological diagnosis of influenza.     

Murine Intestinal Humoral Responses in Chronic Schistosoma mansoni Infections

Specific and non-specific production of immunoglobulins (Ig) by the intestinal mucosa was examined in mice infected with the human blood fluke Schistosoma mansoni. Ileal and colonic mucosal tissue samples were cultured for 2 days, the medium replaced and the culture continued for a further 2 days. Ig concentrations and specific antibodies to soluble schistosome egg antigens in culture supernatants were estimated by isotype-specific ELISA. Cultured mucosae from control mice produced little IgG, but significant amounts of IgA and IgM on prolonged culture. IgG concentrations were increased in infected animals, mainly in the initial culture period, indicative of systemic, rather than local origins. By contrast, significantly increased local production of IgA and IgM occurred after the start of egg deposition in the intestinal mucosae. Although specific anti-egg antibodies of the IgG and IgM class were detected, none of the local IgA response was specific for schistosome eggs. We conclude that specific intestinal immune responses to schistosome eggs reflect systemic responses, whereas locally increased IgA production is largely non-specific. This pattern of response is likely to be related to the prior systemic exposure to schistosome eggs, which results in polyclonal local B-cell activation, but fails to trigger an antigen-specific IgA mucosal response.     

Cross-protection against influenza A virus infection by passively transferred respiratory tract IgA antibodies to different hemagglutinin molecules.

Mice that were intranasally immunized with different influenza A virus hemagglutinins (HA), derived from PR8 (H1N1), A/Yamagata (H1N1) or A/Fukuoka (H3N2) virus, together with cholera toxin B subunit as an adjuvant, were examined for protection against PR8 infection; PR8 HA and A/Yamagata HA immunization conferred complete protection, while A/Fukuoka HA immunization failed to confer protection. In parallel with protection, PR8 HA-, A/Yamagata HA-, and A/Fukuoka HA-immunized mice produced a high, a moderate and a low level of PR8 HA-reactive IgA in the respiratory tract, respectively. These IgA antibodies were not only higher in content in the nasal secretions, but also more cross-reactive than IgG. The purified IgA antibodies from respiratory tract washings of PR8 HA-immunized mice, which contained the HA-specific IgA corresponding to the amount detected in the nasal wash, were able to protect mice from PR8 challenge when transferred to the respiratory tract of naive mice. The transfer of IgA from A/Yamagata HA-immunized mice also afforded cross-protection against PR8 infection, whereas the IgA from A/Fukuoka HA-immunized mice failed to provide protection. The ability of transferred IgA to prevent viral infection was dependent on the amount of HA-reactive IgA remaining in the respiratory tract of the host at the time of infection. These experiments directly demonstrate that IgA antibodies to influenza A virus HA by themselves play a pivotal role in defence not only against homologous virus infection, but also against heterologous drift virus infection at the respiratory mucosa, the portal of entry for the viruses.     

Development and persistence of local and systemic antibody responses in adults given live attenuated or inactivated influenza A virus vaccine.

An enzyme-linked immunosorbent assay was used to measure nasal-wash and serum isotype-specific hemagglutinin antibody responses in 109 seronegative (hemagglutination-inhibiting titer less than or equal to 1:8) adults vaccinated intranasally with live attenuated A/Washington/897/80 (H3N2) or A/California/10/78 (H1N1) cold-adapted (ca) virus or with licensed subvirion vaccine subcutaneously. Live and inactivated virus elicited serum immunoglobulin A (IgA) responses in 83 and 96% of vaccinees, respectively, and elicited serum IgG responses in 72 and 100% of vaccinees. Inactivated virus induced higher titers of serum antibodies than did live virus and stimulated a nasal-wash IgG response more often than did live virus (94 versus 59%, P less than 0.01). In contrast, only 38% of inactivated virus vaccinees had local IgA responses compared with 83% of live virus vaccinees. Serum IgA and IgG and nasal IgG antibody titers remained elevated above prevaccination levels for at least 6 months in most of the live and inactivated vaccine responders, but the mean level of local IgA antibody induced by infection with live virus vaccine, in particular, decreased substantially. Considered in the context of previous work, the finding that live virus vaccine induced relatively long-lasting antibody in both local and serum compartments suggested that this vaccine may be a suitable alternative to inactivated vaccine for use in healthy persons.     

Local antibody production and respiratory syncytial virus infection in children with leukaemia

Children undergoing therapy for acute lymphoblastic leukaemia (ALL) are at increased risk of severe viral respiratory infection, and some find it difficult to terminate virus secretion. This increased severity may result from a defect in the mucosal immune response. To test this hypothesis, nasal immunoglobulin secretion and specific antiviral antibody responses to infection with respiratory syncytial (RS) virus in children with ALL have been compared with those in a normal age-matched comparison group. Children with leukaemia secreted normal levels of IgA and slightly raised IgM levels. IgG levels were depressed. Following RS virus infection, the majority of children with leukaemia secreted normal amounts of IgA and IgG nasal antibody and successfully cleared the virus. However, three of the 13 children studied made poor or undetectable nasal antibody responses, which correlated with their inability to clear the virus.     

Immunization with the binding domain of FimH, the adhesin of type 1 fimbriae, does not protect chickens against avian pathogenic Escherichia coli.

The aim of this study was to investigate whether vaccination with the sugar-binding domain of FimH (FimH156) was able to protect chickens against avian pathogenic Escherichia coli (APEC). FimH156 was expressed and purified using Ni-NTA affinity chromatography. Binding of FimH156 to mannosylated bovine serum albumin demonstrated that the protein retained its biological activity. Moreover, anti-FimH156 antisera were able to inhibit in vitro binding of E. coli to mannosylated bovine serum albumin. In a first vaccination experiment, FimH156 was administered intramuscularly as a water-in-oil emulsion to specific pathogen free broiler chicks. A predisposing infection with the Newcastle disease virus strain Lasota was administered 3 weeks later, followed 3 days later by an aerosol challenge with the virulent APEC strain CH2. A good anti-FimH156 immunoglobulin (Ig)G immune response was detected in serum, but no protective effects of FimH156 against APEC were seen. In a second experiment, SPF chicks were vaccinated intramuscularly or intranasally with FimH156. Booster vaccinations were administered 20 days later. While the intramuscular immunization yielded a strong IgG response in the serum and trachea, no significant IgA response could be detected in tracheal washes. Intranasal immunization did not yield a significant IgG or IgA response in serum and trachea. No protective effects of the FimH156 could be detected, confirming the results of the first experiment. Thus, although the FimH156 induced a strong immune response, it was unable to protect chickens against APEC.     

Analysis of rabbit lung lavage immunoglobulins during the course of pulmonary inflammation induced with aerosolized antigen

Lung lavage fluids (LLF) from rabbits with pigeon dropping extract (PDE)-induced granulomatous pulmonary inflammation were studied for protein and immunoglobulin (Ig) G and A levels. It was found that the protein levels of the lung fluids of rabbits increased to a maximum after 2-3 weeks of aerosol treatment with PDE during which time inflammation of the lung increases. This is followed by a gradual decrease in protein content as the inflammation wanes and the lung returns to normal. These variations primarily reflect changes in IgG and IgA levels. IgG and IgA levels follow different courses. IgA reaches a maximum in the first week of inflammation and then gradually decreases. In contrast, IgG reaches a maximum level (2-3 weeks) and stays at an elevated level throughout the 12 week period of aerosol treatment with PDE. Antibodies to PDE in these two classes of immunoglobulins do not entirely reflect the immunoglobulin class levels. IgA antibody levels reach a maximum after extended aerosol challenge while IgG antibody reaches a maximum early and then declines to background levels. The specificity of the non-PDE antibody IgG is unknown at present. The distribution of IgA subclass producing cells in the lung is different than in the gut. In the lung the major subclass is g while in the gut it is f. The distribution of subclasses of IgA in the LLF, however, does not appear to reflect the cellular distribution. The reason for this is not clear.     

Immunoglobulin G subclass antibody responses in influenza A and parainfluenza type 1 virus infections

Antibody responses in immunoglobulin G1, G2, G3, G4, A (IgA1) and M isotypes were studied in 10 patients with an acute influenza A and in another 10 patients with a parainfluenza type 1 virus infection using radioimmunoassay with standardized monoclonal anti-immunoglobulins. A four-fold or greater increase of antibody in patients have an acute influenza A virus infection, were found in IgG1 (all 10 cases), IgG3 (seven cases), IgG4 (eight cases) and in IgA1 (six cases) whereas IgG2 and IgM responses were observed only in one and three cases, respectively. The antibody titre values were converted to immunoglobulin units by multiplying the titre by a pre-determined correction coefficient compensating for the varying affinity of the individual monoclonal anti-immunoglobulins. These units were then used to calculate the actual proportions of each isotype. In the convalescent phase, 78% of total anti-influenza A antibodies were estimated to be of IgG1 isotype and other immunoglobulin isotypes varied from 3 to 7% of total. Similar results in parainfluenza virus antibodies were obtained with serum pairs from patients with an acute parainfluenza virus infection.