Serum bactericidal activity in a secondary school population following an outbreak of meningococcal disease: effects of carriage and secretor status

Abstract Sera obtained from 106 children following an outbreak of Neisseria meningitidis (B:4:P1.15) were screened for bactericidal antibodies against isolates of meningococci and Neisseria lactamica . Most had high titres of antibodies to N. lactamica and N. meningitidis NG:4:- but not to capsulate isolates: B:4:P1.15; B:15:P1.16; B:4:-; C:4:-. Bactericidal activity was higher for both carriers and secretors but the differences were not significant. Bactericidal activity was not associated with total or specific IgA or IgM. Carriers had significantly higher levels of IgG to N. lactamica but not to NG:4:- in sera with bactericidal activity for each of the capsulate strains. Among non-carriers, higher levels of IgG to N. lactamica were associated with killing of B:4:P1.15 and B:4:-. Secretors' sera with bactericidal activity had significantly higher levels of IgG to N. lactamica compared with sera that were not bactericidal. This was not observed among non-secretors. Antibodies to the outbreak strain were adsorbed by all Neisseria isolates tested and absorption of sera with N. lactamica alone completely removed the bactericidal activity against the outbreak strain.     

Salivary immunoglobulin classes in Nigerian smokers with periodontitis

AIM:To determine the levels of salivary immunoglobulin classes in Nigerian smokers and non-smokers with periodontitis.METHODS:Sixty-nine individuals were recruited into this study after obtaining informed consent.They were subdivided into three groups that consisted of 20(aged 46 ± 11 years) cigarette smokers with periodontitis(S+P);24(40 ± 12 years) smokers without periodontitis(S-P);and 25(53 ± 11 years) non-smokers with periodontitis(NS+P).An oral and maxillofacial surgeon used radiographs for periodontal probing for the diagnosis of periodontitis.The smokers included subjects who smoked at least six cigarettes per day and all the periodontitis patients were newly diagnosed.About 5 mL of unstimulated saliva was expectorated by each subject into plain sample bottles.Salivary immunoglobulin levels were estimated using enzyme linked immunosorbent assay.Student's t test was used to deter-mine significant differences between the means.Values of P 0.05 were regarded as significant.RESULTS:No significant differences were observed in the mean salivary levels of the immunoglobulin classes(IgG,IgA,IgM and IgE) when S+P was compared with S-P.Mean salivary levels of IgA(520.0 ± 155.1 ng/mL vs 670.0 ± 110 ng/mL,P = 0.000) and IgM(644.5 ± 160.0 ng/mL vs 791.4 ± 43.7 ng/mL,P = 0.000) were significantly lower in the S+P compared with NS+P group.Salivary IgA(570.4 ± 145.6 ng/mL vs 670.0 ± 110 ng/mL,P = 0.008) and IgM(703.1 ± 169.3 ng/mL vs 791.4 ± 43.7 ng/mL,P = 0.012) levels were significantly lower in the S-P compared with NS+P group.Only one(5%) periodontal patient had detectable levels of salivary IgE(0.20 IU/mL).Similarly,only one smoker(4.17%) had detectable levels of salivary IgE(0.04 IU/mL) and two non-smokers(9.52%) had detectable levels of IgE(0.24 IU/mL).CONCLUSION:Our study suggests that reduced salivary IgA and IgM levels in smokers with periodontitis could enhance increased susceptibility to periodontitis.     

Analysis of paraprotein transport into the saliva by using anti-idiotype antibodies

To determine the extent of clonal involvement of the secretory immune system and the origin of salivary immunoglobulins (Ig) in monoclonal gammopathy patients, saliva and serum samples were collected from five affected individuals (two IgA myelomas, one IgG myeloma, one IgG benign monoclonal gammopathy, and one IgM lymphoma) and were assayed for the presence of monoclonal Ig. Purified polyclonal or monoclonal anti-idiotype (Id) antibodies were prepared against each of the isolated serum paraproteins. In all five individuals, the patient saliva samples inhibited the binding of 125I-labeled homologous Ig to the corresponding anti-Id antibodies, but normal saliva did not. The concentration of Id in patients' saliva varied from 1 to 400 micrograms/ml; i.e., 0.004 to 1.0% of the corresponding serum values. Saliva of a lymphoma patient whose IgM kappa protein exhibited rheumatoid factor (RF) activity also contained RF. The salivary Id-bearing molecules were found to have the same Ig isotype as the serum paraproteins. The myeloma IgA represented a minor component (0.4 and 3.9%) of the total salivary IgA. The salivary IgA myeloma proteins were associated at least in part with secretory component, but the salivary IgG paraproteins were not. In an IgA myeloma patient, a minority (17%) of the IgA+ plasma cells found in the lacrymal gland biopsy specimen were Id+, whereas the great majority (98%) of bone marrow IgA plasma cells were Id+. The results suggest active transport rather than passive transudation of myeloma IgA into the patients' saliva, and the integrity of the secretory immune system was not compromised by the neoplastic process.     

The determination in saliva of IgA antibodies to Shigella ribosomes for the diagnosis of dysentery

The levels of antiribosomal antibodies to Shigella ribosomes in serum and saliva samples from 38 dysentery patients (15 S. sonnei cases and 23 S. flexneri cases), 14 patients with salmonellosis and 136 healthy adults were determined in ELISA with ribosomes from S. sonnei R-mutant used as solid-phase antigen. High levels of "normal" antiribosomal IgA, IgG and IgM antibodies were revealed in the sera of healthy persons while the level of salivary IgA antibodies was very low. In dysentery infection no increase in the levels of serum IgG and IgM antibodies and only a slight increase in the level of IgA antibodies were revealed. Local immune response was manifested by the early (on days 2-4 from the onset of infection) and significant augmentation (12- to 16-fold) of salivary antiribosomal IgA antibodies. An increase in the level of these antibodies was registered in 95-100% of dysentery patients but not in patients with salmonellosis, which made it possible to recommend the method for diagnosing shigellosis. Immune response to Shigella ribosomal antigens, in contrast to the response induced by Shigella O-antigen, is almost exclusively local.     

Non-secretion of blood group antigens and susceptibility to infection by Candida species

One of the innate defences against superficial infections by Candida species appears to be the ability of an individual to secrete the water-soluble form of his ABO blood group antigens into body fluids. There was a significantly higher number of non-secretors (48.9%) among 174 patients with either oral or vaginal candida infections compared with the proportion of non-secretors in the local population (26.6%). The protective effect afforded by the secretor gene might be due to the ability of glycocompounds in the body fluids of secretors to inhibit adhesins on the surface of the yeast. In attachment studies, preincubation of blastospores with boiled secretor saliva significantly reduced their ability to bind to epithelial cells. Non-secretor saliva did not reduce the binding and often enhanced the numbers of attached yeasts. Possible host-parasite interactions underlying the susceptibility of non-secretors to candida and other infections are discussed.     

Non-secretion of blood group antigens and susceptibility to infection by Candida species

Abstract One of the innate defences against superficial infections by Candida species appears to be the ability of an individual to secrete the water-soluble form of his ABO blood group antigens into body fluids. There was a significantly higher number of non-secretors (48.9%) among 174 patients with either oral or vaginal candida infections compared with the proportion of non-secretors in the local population (26.6%).
The protective effect afforded by the secretor gene might be due to the ability of glycocompounds in the body fluids of secretors to inhibit adhesins on the surface of the yeast. In attachment studies, preincubation of blastospores with boiled secretor saliva significantly reduced their ability to bind to epithelial cells. Non-secretor saliva did not reduce the binding and often enhanced the numbers of attached yeasts.
Possible host-parasite interactions underlying the susceptibility of non-secretors to candida and other infections are discussed.     

Relationship between secretion of the Anton blood group antigen in saliva and adherence of Haemophilus influenzae to oropharynx epithelial cells

Inhibition of adherence of bacteria to epithelial cells contributes to a reduction of infections by these bacteria. We have shown that the Anton blood group antigen, the erythrocyte receptor for Haemophilus influenzae (van Alphen et al. 1986, FEMS Microbiol. Lett. 37, 69-71), occurs in saliva, that the occurrence is not related to the secretor state of the donor of the saliva and that saliva containing Anton antigen could not inhibit the adherence of H. influenzae to oropharynx epithelial cells. Anton antigen was detected in saliva samples of 14 donors by immunoblotting with two different anti-Anton sera. The amount of Anton antigen correlated with the ability of H. influenzae to adhere to the epithelial cells of the donor of the saliva: 4.1 +/- 0.1 Anton antigen units for donors with more than 50 H. influenzae per cell and 1.6 +/- 0.5 units for donors with less adhering epithelial cells. No correlation between the amount of Anton antigen in saliva and secretor status of the donor was observed. Adherence of H. influenzae to epithelial cells was not inhibited by saliva of secretors (N = 11) or non-secretors (N = 3). The same saliva did not inhibit the interaction of the bacteria with Anton antigen bearing erythrocytes as measured by haemagglutination inhibition. This indicates that the amount of Anton antigen in saliva is probably too low to interfere with the interaction of H. influenzae with oropharynx epithelial cells and erythrocytes.     

Relationship between secretion of the Anton blood group antigen in saliva and adherence of Haemophilus influenzae to oropharynx epithelial cells

Abstract Inhibition of adherence of bacteria to epithelial cells contributes to a reduction of infections by these bacteria. We have shown that the Anton blood group antigen, the erythrocyte receptor for Haemophilus influenzae (van Alphen et al. 1986, FEMS Microbiol. Lett. 37, 69–71), occurs in saliva, that the occurrence is not related to the secretor state of the donor of the saliva and that saliva containing Anton antigen could not inhibit the adherence of H. influenzae to oropharynx epithelial cells.
Anton antigen was detected in saliva samples of 14 donors by immunoblotting with two different anti-Anton sera. The amount of Anton antigen correlated with the ability of H. influenzae to adhere to the epithelial cells of the donor of the saliva: 4.1 ± 0.1 Anton antigen units for donors with more than 50 H. influenzae per cell and 1.6 ± 0.5 units for donors with less adhering epithelial cells. No correlation between the amount of Anton antigen in saliva and secretor status of the donor was observed. Adherence of H. influenzae to epithelial cells was not inhibited by saliva of secretors ( N = 11) or non-secretors ( N = 3). The same saliva did not inhibit the interaction of the bacteria with Anton antigen bearing erythrocytes as measured by haemagglutination inhibition. This indicates that the amount of Anton antigen in saliva is probably too low to interfere with the interaction of H. influenzae with oropharynx epithelial cells and erythrocytes.     

Comparison of oligosaccharides derived from salivary mucin of Japanese secretor and non-secretor individuals of blood group type-A

Comparison of oligosaccharide components derived from salivary mucin was performed between secretor and non-secretor individuals. Salivary mucin was collected from four secretors and three non-secretors having blood group type-A. Compositional analysis showed that the contents of galactose and N-acetylglucosamine in the non-secretor were higher than those in the secretor. The O-linked oligosaccharides obtained by treatment with alkaline borohydride were separated by gel filtration using Sephadex G-50. The results indicated that the size of the type-A active oligosaccharides from the secretor was similar to or smaller than that of the non-secretor. Ion-exchange chromatography showed that the secretors had strong type-A activities in both the neutral and acidic fractions but the non-secretors showed type-A activity mainly in the neutral fraction. These results suggest that compositional differences in blood group substances exist between secretors and non-secretors.     

The utility of saliva for the assessment of anti-pneumococcal antibodies: investigation of saliva as a marker of antibody status in serum

Context: Salivary antibodies may act as non-invasive marker of systemic immunity enabling assessment of vaccination and protection against bacterial infections.

Objective: To assess if levels of anti-pneumococcal (Pn) antibodies in saliva reflect concentrations in serum and determine whether saliva can accurately identify protective concentrations in serum.

Methods: IgG, IgA and IgM antibody levels in paired saliva and serum samples were measured against 12 Pn polysaccharide antigens in 72 healthy adults.

Results: Antibody levels in saliva correlated positively with serum across immunoglobulin classes, most strongly for IgA. Individuals who had protective antibody levels in serum demonstrated significantly higher IgG and IgA salivary antibody concentrations/secretion rates. Salivary IgG and IgA Pn antibodies were able to distinguish between those with/without protective levels in serum for the majority of serotypes. Salivary IgM antibodies were not able to differentiate protective status. Median IgG and IgA Pn salivary parameters were able to identify individuals who had protective levels in serum on ≥8/12 serotypes with moderate accuracy: median IgA secretion rates provided the best sensitivity (73%) and specificity (71%).

Conclusions: These findings suggest that IgG and IgA Pn specific antibodies in saliva may be useful surrogate markers of antibody status in serum.     

Influence of the blood group reactive substances in saliva on the aggregation of Streptococcus rattus

The interaction of blood group reactive substances in saliva with bacteria was investigated by testing saliva from persons with different blood groups in a bacterial aggregation assay with Streptococcus rattus HG 59, originally S. rattus BHT. For blood group A, saliva from 10 persons out of 11 aggregated S. rattus and for blood group O, saliva from 10 persons out of 16 aggregated S. rattus. For blood group B, saliva from 6 persons out of 8 aggregated S. rattus weakly and the average aggregation activity of blood group B was much lower than for blood group A or O. In addition, saliva from 3 non-secretors did not aggregate S. rattus. The role of blood group antigens in bacterial aggregation was confirmed by inhibition studies with blood group specific sugars and various other sugars. GalNAc, specific for blood group A, inhibited bacterial aggregation by saliva whereas D-galactose, specific for blood group B, and D-fucose, specific for blood group O, did not. In addition, sialic acid, a major terminal sugar residue in mucins, also inhibited the bacterial aggregation. This study shows that the blood group and secretor status of a person may influence the interaction of saliva with bacteria in the oral cavity.     

Immunodiagnosis of Dengue Virus Infection Using Saliva

Keeping in view the complications and the case fatality associated with dengue virus, several serologic tests have been developed. However, the major drawback of these serologic tests is the need for a venous blood sample obtained by invasive venipuncture. As a noninvasive alternative, saliva provides a body fluid that contains antibodies of diagnostic importance. Hence, the detection of DEN-specific IgM and IgG antibodies in serum and saliva from 80 patients was compared. Salivary IgM antibodies were detected in 100% of the serum IgM-positive samples and in 30% of the serum samples that were negative for IgM antibodies. Salivary IgG antibodies were detected in 93.3% of the serum samples that were positive for anti-dengue IgG antibodies and in none of the serum IgG-negative cases. None of the specimens from the healthy controls showed the presence of IgM or IgG antibodies. The detection of both IgG and IgM antibodies in saliva correlated well with the serum IgG and IgM detection by the ELISA test (r = 0.6322 and r = 0.4227). Detection of salivary IgM antibodies by ELISA showed 100% sensitivity, 70% specificity, 90.9% positive predictive value, and 100% negative predictive value. The detection of IgG in saliva proved to be a promising tool as the sensitivity, specificity, positive predictive value, and negative predictive value were found out to be 93.3%, 100%, 100%, and 83.3%, respectively. Thus, from this study we conclude that the detection of DEN-specific salivary IgG and IgM antibodies are useful markers for dengue infection.     

IgA and IgM anti-Naegleria fowleri antibodies in human serum and saliva

Antibodies from IgA and IgM classes that recognize Naegleria fowleri (Nf) proteins were detected by the ELISA assay in serum and saliva from three groups of people: (i) subjects with upper respiratory tract infections (URTI) living in the parasite-endemic area, (ii) healthy persons from the same area, and (iii) healthy persons from a parasite-nonendemic area. In serum and in saliva the titers of IgA antibodies to Naegleria fowleri in the group of patients with URTI was significantly higher than that of the healthy group in the parasite-endemic area; also the titers of IgM antibodies in serum were significantly higher in patients. On the contrary, in saliva the antibodies were higher in healthy people from the parasite-endemic area. In all cases the subjects from the parasite-nonendemic area had lower antibody titers in serum and saliva.     

One year in Antarctica: mucosal immunity at three Australian stations

The effect of a year's isolation in Antarctica on the human mucosal immune system was assessed during the winter of 1992 at three Australian Antarctic stations: Casey, Davis and Mawson. Saliva samples were collected from each expeditioner prior to their departure from Australia and during each month in Antarctica. The concentrations of salivary immunoglobulins IgA and IgG were significantly different between the three stations, but there were no differences for salivary IgM and albumin. The mean concentrations of IgA were higher at Mawson (P < 0.008), and the mean concentrations of IgG were lower at Davis (P < 0.001) compared with the other stations. Ranges of values observed at the stations over the 12-13 months were similar. The variability of values within individuals showed station differences for salivary IgM and IgG only. The study revealed significant changes in salivary immunoglobulin values over the period in Antarctica, with similar patterns at the three Australian stations. The salivary IgA and IgM levels were lower in the first 4 months in Antarctica (January-April) and increased to maximum values in July-August, before returning to mean levels when isolation was broken in October-November. The patterns of salivary IgA and IgM suggest that stressors due to isolation may play a role in alterations of mucosal immunity in expeditioners in Antarctica.     

Trends in mucosal immunity in Antarctica during six Australian winter expeditions

The mucosal immune status of Australian Antarctic personnel was monitored during six wintering expeditions at two Australian Antarctic Research Stations, Casey in 1992, 1993, 1994, and Mawson in 1992, 1995, 1996. Salivary immunoglobulin and albumin levels were examined for differences between stations and expeditions, and for monthly changes over the expedition year. Salivary IgA and IgM concentrations were on average higher for the 1993 Casey expeditioners, and all salivary protein levels were lower for 1996 Mawson expeditioners compared to levels of the other expeditions. The change in salivary IgA and IgM concentrations over the 1-year period revealed a consistent pattern between expeditions. Salivary IgA levels were lower in March, April and May compared to other months of the year (P = 0.0002). Salivary IgM levels were lowest in the first 4 months of the year, with peak levels in June and July (P < 0.0001). There were no changes in salivary IgG and albumin concentrations over the expedition year. Though the cause of the changes in salivary IgA and IgM levels over the year is unknown, the changes could reflect alterations in mucosal immunity in response to stressors associated with isolation.     

Isotypic analysis of specific antibody response in serum, saliva, gastric and rectal homogenates of Helicobacter pylori-infected patients

Abstract The relationship between systemic and local humoral immune response to Helicobacter pylori is poorly understood. To further address this issue we measured, using ELISA, H. pylori -specific IgG and IgA antibodies in serum, saliva, gastric and rectal homogenates of H. pylori -infected patients. A total of 107 patients who underwent upper GI endoscopy and/or sigmoidoscopy were studied. The isotypic pattern of H. pylori -specific antibodies appeared to differ at the serum, salivary, gastric and rectal mucosa level. Serum H. pylori IgG titers were higher than those of the serum-specific IgA. On the contrary, in saliva samples. H. pylori IgA titers were higher than specific IgG titers. In gastric homogenates, specific IgG and IgA titers were similar. H. pylori -specific IgG were detectable in rectal homogenates but no or very low H. pylori -specific IgA were found in the same material. Furthermore, no difference was found in H. pylori IgG and IgA in serum, saliva and gastric homogenates between duodenal ulcer and non-ulcer dyspepsia patients. Data of the present study indicate that, in H. pylori -infected patients, the specific immune response is as follows: (1) it involves the secretory immune system; (2) it is paralleled by the specific salivary IgA; (3) it does not differentiate duodenal ulcer from non-ulcer dyspepsia patients; and (4) it does not take place in the large bowel.     

ABO blood group and secretor status in the spondyloarthropathies

The postulated role of infectious agents, genetic susceptibility of the host to infection and their interaction in the pathogenesis of ankylosing spondylitis, other spondyloarthropathies, and the associated primary (non-arthritic) diseases are reviewed. Compared with a local control population there is a significantly increased prevalence of non-secretors amongst different groups of patients with spondyloarthropathy: ankylosing spondylitis, reactive arthritis and psoriatic arthropathy. No differences between secretor and non-secretor patients with respect to serum and salivary IgA levels, the occurrence of eye lesions or peripheral joint disease have been found. There is no evidence that ankylosing spondylitis or other spondyloarthropathies are associated with any particular ABO blood group. The association between non-secretion and ankylosing spondylitis strengthens the hypothesis that ankylosing spondylitis has an infective aetiology. It also suggests several pathogenetic mechanisms which may be relevant to the initial host-parasite interactions in the spondyloarthropathies.     

Salivary Immune Responses to the 7-Valent Pneumococcal Conjugate Vaccine in the First 2 Years of Life

Background

The CRM197-conjugated 7-valent pneumococcal vaccine (PCV7) is protective against vaccine serotype disease and nasopharyngeal carriage. Data on PCV7-induced mucosal antibodies in relation to systemic or natural anticapsular antibodies are scarce.

Methods

In a randomized controlled setting, children received PCV7 at age 2 and 4 months (2-dose group), at age 2, 4 and 11 months (2+1-dose group) or no PCV7 (control group). From 188 children paired saliva samples were collected at 12 and 24 months of age. From a subgroup of 15 immunized children also serum samples were collected. IgG and IgA antibody-levels were measured by multiplex immunoassay.

Results

At 12 months, both vaccine groups showed higher serum and saliva IgG-levels against vaccine serotypes compared with controls which sustained until 24 months for most serotypes. Salivary IgG-levels were 10–20-fold lower compared to serum IgG, however, serum and saliva IgG-levels were highly correlated. Serum and salivary IgA-levels were higher in both vaccine groups at 12 months compared with controls, except for serotype 19F. Higher salivary IgA levels remained present for most serotypes in the 2+1-dose group until 24 months, but not in the 2-dose group. Salivary IgA more than IgG, increased after documented carriage of serotypes 6B, 19F and 23F In contrast to IgG, salivary IgA-levels were comparable with serum, suggesting local IgA-production.

Conclusions

PCV7 vaccination results in significant increases in salivary IgG and IgA-levels, which are more pronounced for IgG when compared to controls. In contrast, salivary anticapsular IgA-levels seemed to respond more to natural boosting. Salivary IgG and IgA-levels correlate well with systemic antibodies, suggesting saliva might be useful as potential future surveillance tool.     

Systemic immunization with pneumococcal polysaccharide vaccine induces a predominant IgA2 response of peripheral blood lymphocytes and increases of both serum and secretory anti-pneumococcal antibodies

Ig class-, and IgA and IgG subclass-specific immune responses to a 23 valent pneumococcal polysaccharide vaccine were studied at a single-cell level in the peripheral blood of systemically immunized adults. With a solid phase enzyme-linked immunospot (ELISPOT) assay, PBMC from immunized individuals were assayed for spontaneous Ag-specific antibody (Ab) production before, and on days 7, 14, and 28 after vaccination. On the day of immunization, no spontaneous Ag-specific Ab-secreting cells could be detected. On day 7 after vaccination, a high frequency of cells secreting Ab specific for pneumococcal polysaccharides (PPS) was observed. The IgA class comprised 79% (geometric mean) of the Ag-specific Ab-secreting cells, whereas IgG- and IgM-secreting cells accounted for 12% and 9%, respectively. The majority of Ag-specific IgA-secreting cells produced Ab of the IgA2 isotype. Serum, saliva, and tears collected before and on days 7, 14, and 28 after vaccination were assayed for specific Ab to the vaccine (anti-PPS Ab) by an ELISA. Serum IgA anti-PPS Ab showed the highest increase after vaccination with a 19-fold increase (geometric mean) which peaked on day 14. However, the ratio of Ag-specific polymeric vs monomeric IgA did not change after immunization. Serum IgG and IgM anti-PPS Ab displayed mean increases of 5.5-fold and 5.6-fold, respectively, on day 14. The most pronounced increase of salivary anti-PPS Ab was observed in the IgG class (4.5-fold on day 28) followed by IgM (4-fold on day 28), IgA (2.0-fold on day 14), IgA1 (2.4-fold on day 14) and IgA2 (2.0-fold on day 14). The levels of total IgA, IgG, and IgM in saliva did not change significantly throughout the course of immunization. IgG and IgM anti-PPS Ab levels in tears increased less than in saliva, whereas IgA behaved similarly as in saliva. There were no significant differences in the Ag-specific increase rates between the IgA, IgG, and IgM isotypes in tears.     

Salivary IgA subclasses and infection risk in elite swimmers.

The concentrations of total IgA, IgA1 and IgA2 were measured in saliva collected from 25 elite swimmers in the early and late phases of a 7 month training season and compared with the number of respiratory infections during the season. The IgA1 concentrations in the early phase of the training season were significantly associated (P = 0.01) with the number of respiratory infection episodes during the training season. The lower the concentration of IgA1, the greater the number of infection episodes. Swimmers with four or more infections during the training season had significantly lower salivary IgA1 concentrations than those with less than four infection episodes (P = 0.01). The proportion of IgA1 in the saliva of the elite swimmers (80%) was higher than for normal non-exercising adults (60%). A small proportion of athletes had salivary IgA2 concentrations below the detection limit of the assay and the mean concentration of IgA2 was significantly lower than the concentrations for a normal adult population (P = 0.01). This study suggests that measurement of IgA subclasses, in particular IgA1, at the commencement of a training season may predict infection risk in elite swimmers.