Diagnosis of dengue virus infection by detection of specific immunoglobulin M (IgM) and IgA antibodies in serum and saliva

To evaluate alternative approaches to the serological diagnosis of dengue virus (DEN) infection, the detection of DEN-specific immunoglobulin M (IgM) and IgA antibodies in serum and saliva specimens was assessed in 147 patients with symptoms of DEN infection seen at the Ministry of Health in Nicaragua. Seventy-two serum samples were determined to be positive for anti-DEN antibodies by IgM capture enzyme-linked immunosorbent assay, the routine diagnostic procedure. Serum and saliva specimens were obtained from 50 healthy adults as additional controls. IgM was detected in the saliva of 65 of the 72 serum IgM-positive cases, 6 of the 75 serum IgM-negative cases, and none of the control group, resulting in a sensitivity of 90.3% and a specificity of 92.0% and demonstrating that salivary IgM is a useful diagnostic marker for DEN infection. Detection of IgA in serum may be another feasible alternative for the diagnosis of DEN infection, with serum IgA found in 68 (94.4%) of the IgM-positive cases. In contrast, detection of IgA in saliva was not found to be a useful tool for DEN diagnosis in the present study. Further studies of the kinetics of antibody detection in another set of 151 paired acute- and convalescent-phase serum samples showed that DEN-specific IgA antibodies were detected in more acute-phase samples than were IgM antibodies. Thus, we conclude that DEN-specific IgA in serum is a potential diagnostic target. Furthermore, given that saliva is a readily obtainable, noninvasive specimen, detection of DEN-specific salivary IgM should be considered a useful, cheaper diagnostic modality with similar sensitivity and specificity to IgM detection in serum.     

Diagnosis of Dengue Virus Infection by Detection of Specific Immunoglobulin M (IgM) and IgA Antibodies in Serum and Saliva

To evaluate alternative approaches to the serological diagnosis of dengue virus (DEN) infection, the detection of DEN-specific immunoglobulin M (IgM) and IgA antibodies in serum and saliva specimens was assessed in 147 patients with symptoms of DEN infection seen at the Ministry of Health in Nicaragua. Seventy-two serum samples were determined to be positive for anti-DEN antibodies by IgM capture enzyme-linked immunosorbent assay, the routine diagnostic procedure. Serum and saliva specimens were obtained from 50 healthy adults as additional controls. IgM was detected in the saliva of 65 of the 72 serum IgM-positive cases, 6 of the 75 serum IgM-negative cases, and none of the control group, resulting in a sensitivity of 90.3% and a specificity of 92.0% and demonstrating that salivary IgM is a useful diagnostic marker for DEN infection. Detection of IgA in serum may be another feasible alternative for the diagnosis of DEN infection, with serum IgA found in 68 (94.4%) of the IgM-positive cases. In contrast, detection of IgA in saliva was not found to be a useful tool for DEN diagnosis in the present study. Further studies of the kinetics of antibody detection in another set of 151 paired acute- and convalescent-phase serum samples showed that DEN-specific IgA antibodies were detected in more acute-phase samples than were IgM antibodies. Thus, we conclude that DEN-specific IgA in serum is a potential diagnostic target. Furthermore, given that saliva is a readily obtainable, noninvasive specimen, detection of DEN-specific salivary IgM should be considered a useful, cheaper diagnostic modality with similar sensitivity and specificity to IgM detection in serum.     

Platelia-Toxo IgA, a new kit for early diagnosis of congenital toxoplasmosis by detection of anti-P30 immunoglobulin A antibodies.

With the aim of achieving earlier diagnosis of congenital toxoplasmosis, anti-P30 immunoglobulin A (IgA) antibodies were assayed by using a Platelia-Toxo IgA kit with samples from 72 children born to mothers who seroconverted during pregnancy. A total of 148 serum samples and 1 cerebrospinal fluid samples were from 23 congenitally infected children (2 serum samples were collected from fetuses), and 74 serum samples were from 49 uninfected children. Among the 23 infected children, anti-P30 IgA antibodies were present in all infants either at birth or in the following weeks, whereas anti-P30 IgM antibodies were present in 13 from the 23 infected children either at birth or in the following weeks. Serum samples collected in utero from two infected children were also tested. One of these samples was positive for both anti-P30 IgA and anti-P30 IgM antibodies, whereas both children were negative at birth for these antibodies. Neither anti-P30 IgA nor anti-P30 IgM antibodies were detected in 47 of 49 uninfected children. These results suggest that detection of anti-P30 IgA antibodies by the Platelia-Toxo IgA kit is a very effective method for early diagnosis of congenital toxoplasma infection.     

The diagnostic value of serological studies in pediatric patients with acute Mycoplasma pneumoniae infection

BackgroundMycoplasma pneumoniae is a common pathogen of respiratory tract infections in pediatric patients. Serological studies are traditional methods for the diagnosis. However, early diagnosis of M. pneumoniae infections remains problematic. We investigate the value of early serum immunoglobulin A (IgA), in addition to immunoglobulin G (IgG), and immunoglobulin M (IgM) levels, in children infected with M. pneumoniae.MethodsFrom August 2016 to February 2017, we enrolled pediatric patients based on both clinical symptoms and chest x-ray, and confirmed by positive throat culture for M. pneumoniae. Serum titers of M. pneumoniae IgM, IgG, and IgA during the acute phase were checked. All respiratory samples were further analyzed by polymerase chain reaction (PCR). Diagnostic values of different tests were evaluated.ResultsFifty-six patients fulfilled the diagnostic criteria, with a median age of 4.84 years. Most of them (89.3%) were enrolled within 7 days of disease onset. PCR was positive in 71.4% of the study population. Early IgG samples were of limited value in diagnosing M. pneumoniae infection, of which 89.3% showed a negative result. Positive rates of early serum IgA and IgM were 48.2% and 46.4%, respectively. In combination with IgA and/or IgM, the sensitivity increased to 71.4% during their early clinical course.ConclusionsIn the pediatric population, combined serological tests of M. pneumoniae IgA and IgM, offer an accurate method of early diagnosis comparable to that of PCR, and can be an alternative choice for prompt detection of mycoplasma infections when PCR and culture are not available.     

Plasma and Salivary IgA Subclasses and IgM in HIV-1-Infected Individuals

We examined IgA and IgM responses in parotid saliva from human immunodeficiency virus-1 (HIV-1)-infected individuals. Compared to the uninfected controls, levels of salivary secretory IgA2 were significantly increased in HIV-1-infected subjects, with higher levels in those who displayed oral manifestations of HIV-1 infection. Assessed by enzyme immunoassay, about two thirds of the HIV-1-infected individuals tested positive for salivary HIV-1-specific IgA antibodies but not for salivary IgM. No clear correlations between the amount of HIV-1-specific IgA and CD4 counts or plasma viral loads were found. The proportions of HIV-1-specific IgA did not correlate with the levels of total IgA. Determined by Western blot, IgA1 accounted for the majority of anti-HIV-1 IgA antibodies in saliva. Comparisons between the specificities of plasma and salivary IgA directed to HIV-1 proteins revealed the absence of salivary anti-gp41 IgA antibodies, and lower HIV-1-specific reactivity of IgA and IgM were determined in saliva than in plasma.     

Detection of rubella virus-specific immunoglobulin G (IgG), IgM, and IgA antibodies by immunoblot assays.

Immunoblot (IB) assays were developed for detection of rubella virus (RV)-specific immunoglobulin G (IgG), IgM, and IgA antibodies in human serum following natural infection or immunization. IB assays performed under nonreducing conditions were compared with those performed under reducing conditions and with immunoprecipitation assays. Significant loss of antigenicity (greater than 90%) of RV E1 and E2 proteins was observed when IB assays were performed in the presence of 2-mercaptoethanol as compared with assays under nonreducing conditions. In contrast, the antigenicity of RV capsid protein was not influenced by reducing agents. Sensitivity of IB for RV-specific IgG antibodies was determined to be 0.01 IU/ml under nonreducing conditions. In the determination of RV-specific IgM and IgA antibodies by IB, pretreatment of serum with protein G to remove competing high-affinity RV-specific IgG or rheumatoid factor significantly improved assay sensitivity. IB assays were observed to be superior to immunoprecipitation assays in their ability to better define the specificities of RV-specific antibodies and to detect antibodies of all immunoglobulin classes. However, the conformational sensitivity of RV protein antigenicity should be an important consideration in the interpretation of RV-specific antibodies by IB assays.     

Persistence of rubellavirus-specific immunoglobulin M and immunoglobulin A antibodies: investigation of successive serum samples with lowered immunoglobulin G concentration.

The persistence of rubellavirus-specific immunoglobulin (Ig) M and IgA antibodies has been studied in seven patients with primary postnatal rubella infections. Successive blood samples obtained over a period of several years after the onset of disease have been investigated, employing the fluorescent antibody technique and the sucrose gradient centrifugation method. IgM antibodies were found to persist for 4 to 5 weeks after the onset of disease, with only moderate variation being observed with respect to the different patients and the method of investigation being studied. The persistence of IgA antibodies (as examined by the fluorescent antibody technique) varied from a few weeks to several years after the onset of the disease. The detection of IgA antibodies cannot be considered as conclusive for the diagnosis of recent rubella infections.     

Characteristics and roles of severe acute respiratory syndrome coronavirus 2-specific antibodies in patients with different severities of coronavirus 19

The diagnosis of coronavirus 19 (COVID-19) relies mainly upon viral nucleic acid detection, but false negatives can lead to missed diagnosis and misdiagnosis; severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific antibody detection is convenient, safe and highly sensitive. Immunoglobulin (Ig)M and IgG are commonly used to serologically diagnose COVID-19; however, the role of IgA is not well known. We aimed to quantify the levels of SARS-CoV-2-specific IgM, IgA and IgG antibodies, identify changes in them based on COVID-19 severity, and establish the significance of combined antibody detection. COVID-19 patients, divided into a severe and critical group and a moderate group, and non-COVID-19 patients with respiratory disease were included in this study. A chemiluminescence method was used to detect the levels of SARS-CoV-2-specific IgM, IgA and IgG in the blood samples from the three groups. Epidemiological characteristics, symptoms, blood test results and other data were recorded for all patients. Compared to the traditional IgM–IgG combined antibodies, IgA–IgG combined antibodies are more effective for diagnosing COVID-19. During the disease process, IgA appeared first and disappeared last. All three antibodies had significantly higher levels in COVID-19 patients than in non-COVID-19 patients. IgA and IgG were also higher for severe and critical disease than for moderate disease. All antibodies were at or near low levels at the time of tracheal extubation in critical patients. Detection of SARS-CoV-2-specific combined IgA–IgG antibodies is advantageous in diagnosing COVID-19. IgA detection is suitable during early and late stages of the disease. IgA and IgG levels correspond to disease severity.     

Comparison of serum and mucosal antibody responses following severe acute rotavirus gastroenteritis in young children.

The development of mucosal immunity is presumed to be the most important marker of rotavirus infection. The practical difficulties of obtaining small-bowel secretions stimulated this study of the antibody response to acute rotavirus infection at other sites. Forty-four infants admitted to the hospital with rotavirus gastroenteritis had serum, saliva, and feces collected at the acute phase (median, 5.5 days), during convalescence (median, 33.5 days), and 4 months later (median, 12.2 weeks). A subgroup of 19 children also had duodenal juice collected in parallel. Rotavirus-specific immunoglobulin G (IgG), IgA, secretory immunoglobulin, and IgM were measured and compared in all samples. The results showed that the estimation of antirotavirus serum IgM, serum IgG, duodenal juice IgA, and duodenal juice IgM by an enzyme immunoassay indicated an immune response to severe primary rotavirus infection in all children. Four months later, the levels of serum IgG and IgA served as the most sensitive markers of the preceding rotavirus infection. The predictive accuracies of immune responses at different sites in relation to a positive IgA immune response in the duodenum were calculated. Fecal IgA predicted duodenal IgA rotavirus antibodies with accuracies of 86% at 1 month and 92% at 4 months. The high sensitivity of serum IgM and IgG in detecting rotavirus infection and the high predictive accuracy of fecal IgA as an indicator of duodenal IgA abrogates the need for duodenal intubation to detect (or monitor) an immune response to rotavirus infection. This finding has important practical implications for epidemiological studies of acute diarrhea in children and in rotavirus vaccine trials.     

Evaluation of Four Commercial Immunoglobulin G (IgG)- and IgM-Specific Enzyme Immunoassays for Diagnosis of Mycoplasma pneumoniae Infections

The four following commercially available enzyme immunoassays (EIAs) were assessed and compared for their performance in detecting Mycoplasma pneumoniae immunoglobulin G (IgG)- and IgM-specific antibodies Platelia EIA, ImmunoWELL M. pneumoniae ELISA IgG and IgM, ETI-MP-IgG and IgM EIAs and Biotest anti-M. pneumoniae IgG and IgM ELISA (referred to herein as EIA-Platelia, EIA-BMD, EIA-Sorin, and EIA-Biotest). Three groups of patients were investigated: 39 patients (27 children and 12 adults) with respiratory infections who tested positive by PCR for M. pneumoniae in respiratory specimens (group I; 52 serum samples), 61 healthy children and adults (group II; 61 serum samples), and 20 patients with rheumatoid factor or antinuclear antibodies, or who tested positive for antiviral IgM (group III; 20 serum samples). In group III, the IgM specificity for EIA-Platelia, EIA-BMD, EIA-Biotest, and EIA-Sorin was 100, 90, 65, and 25%, respectively. In the children from group I, the four EIAs had similar IgM sensitivities (89 to 92%); the sensitivity for IgG was greater with EIA-BMD and EIA-Biotest than with EIA-Platelia and EIA-Sorin (66 and 78% versus 55 and 52%, respectively). In adult patients from group I, 9 to 10 serum samples were positive for IgG with a concordant sensitivity of 75 to 83% between the four EIAs but a striking difference in IgM sensitivity: 16% by EIA-Platelia and EIA-BMD, 50% by EIA-Biotest, and 58% by EIA-Sorin. Discrepant and unexpected results were observed in IgM detection from control healthy patients using EIA-Sorin and EIA-Biotest, confirming the lack of specificity of these two EIAs and making them inaccurate for routine diagnosis. A good concordance of IgG seroprevalence in healthy adults was found between the four EIAs (66 to 70%), though this concordance was lower with EIA-Platelia (43%). In healthy children, EIA-BMD and EIA-Biotest gave a higher IgG seroprevalence than EIA-Sorin and EIA-Platelia (45% each for the former compared to 17 and 20%, respectively, for the latter). These results confirm that the IgM EIA serology test is a valuable tool for the early diagnosis of M. pneumoniae infections in children, as long as the EIA used is specific. In adults, the difficult interpretation of EIAs suggests that paired sera, combined with PCR detection on respiratory tract specimens collected on admission of patient, should be required for accurate diagnosis.     

Laboratory diagnosis of congenital syphilis by immunoglobulin M (IgM) and IgA immunoblotting.

We screened cord blood or serum samples from 101 infants at risk for congenital syphilis and serum samples from their mothers for immunoglobulin G (IgG), IgM, and IgA antibodies to Treponema pallidum by western blotting (immunoblotting). Clinical evaluation showed that six infants had signs and/or symptoms consistent with congenital syphilis. The sera from five of these infants were IgM blot positive, and four were IgA blot positive. Four asymptomatic infants had serologic evidence of congenital syphilis. The sera from three of these infants were IgM blot positive, and two were IgA blot positive. However, the IgM reactivity of the serum from one asymptomatic infant, which was also IgA positive, was abolished by protein G treatment. An IgM capture enzyme-linked immunosorbent assay corroborated the presence of IgM antibodies in six of seven IgM blot-reactive sera. Overall, for detection of symptomatic congenital syphilis, a sensitivity of 83% for IgM blotting and 67% for IgA blotting was obtained. The significance of positive IgM or IgA Western blots for asymptomatic infants requires further study to confirm infection in these infants.     

Significance of immunoglobulin a titres in the diagnosis of urogenital chlamydial infections

The significance of chlamydial serum IgA compared with IgM and IgG in the diagnosis of urogenital chlamydial infection was evaluated using 120 sera from different categories of patients. In urethritis patients both IgM and IgA antibodies were not found to be present consistently, whereas in patients with deep-seated chlamydial infection, IgA was more often present. Although of limited value in superficial infections, demonstration of IgA antibodies may be of value in the diagnosis of deep-seated chlamydial infections.     

Radioimmunoassay for the detection of virus-specific IgA antibodies in saliva

The use of a sensitive and versatile radioimmunoassay (RIA) for detection of mumps-specific IgA and measles-specific IgA in unconcentrated saliva samples is described. The samples were obtained either by expectoration or by swabbing of the oral cavity, with or without stimulation of secretion, and were inactivated and clarified before testing. Mumps-specific IgA antibodies were detected as early as one day after onset of illness and peaked at 1-2 weeks after onset. Measles-specific salivary IgA antibodies were detected in 15-month old children 2-3 weeks after immunization. These results suggest that the RIA technique may be useful for early diagnosis of viral infections and for confirmation of response to immunization without the need for a blood sample, as well as for the study of the secretory immune response in very young and older subjects.     

Serodiagnosis of respiratory syncytial virus (RSV) infection in children as measured by detection of RSV-specific immunoglobulins G, M, and A with enzyme-linked immunosorbent assay.

The diagnostic value of an enzyme-linked immunosorbent assay for detection of respiratory syncytial virus (RSV)-specific immunoglobulin G (IgG), IgM, and IgA in sera from infants and children with proven RSV infection, from a control group, and from patients with symptoms of viral respiratory disease was analyzed. Compared to virus isolation and RSV antigen detection methods, the sensitivity of this assay was 87% and the specificity was 79%. For IgG alone, these were 45 and 92%, for IgM alone they were 48 and 92%, and for IgA alone they were 74 and 95%, respectively.     

Immunoglobulins G, M, and A against Sporothrix schenckii exoantigens in patients with sporotrichosis before and during treatment with itraconazole

Sporotrichosis is an important subcutaneous mycosis, with an increasing worldwide incidence. However, few data are available regarding the immunological aspects of Sporothrix schenckii infection, particularly the humoral responses to the fungus. In this study we measured immunoglobulin G (IgG), IgM, and IgA in sera from 41 patients with sporotrichosis before antifungal treatment and from another 35 patients with sporotrichosis during itraconazole treatment by using a recently described S. schenckii exoantigen enzyme-linked immunosorbent assay (ELISA). More than 95% of patients had detectable IgA antibodies, and more than 85% had IgM and IgG antibodies before treatment. The number of patients with IgG antibodies increased to 91% during treatment. Conversely, significantly fewer samples from treated patients were positive for IgM (71%) and IgA (89%). Overall, 78% of patients had detectable levels of all isotypes tested at diagnosis, and this percentage dropped to 62.9% in patients receiving itraconazole. Testing of all three isotypes improved the sensitivity; at least two isotypes were detected in 93% of patients before and 89% after treatment. The reactivity of 94 sera from patients with other diseases and healthy individuals was also tested. Cross-reactivity occurred in 33% of the heterologous sera. Most of them were positive only in one isotype, 8.5% were positive for at least two isotypes, and only one serum (1.1%) was positive for the three isotypes. Antibodies produced during S. schenckii infection are diverse, and we demonstrate that an exoantigen ELISA for the detection of combinations of IgA, IgG, and IgM antibodies is a highly sensitive and specific diagnostic assay for sporotrichosis.     

Failure of serology in diagnosing chlamydial infections of the female genital tract.

Chlamydia trachomatis was recoved from 20% (36/180) of women attending a venereal disease clinic. All infected women had chlamydial antibodies in their serum and cervical secretions. However, the background rates of chlamydial antibody in chlamydia-negative women were very high. Measurement of antibodies in serum (complement fixation or immunoglobulin G [IgG] and IgM by microimmunofluorescence) or cervical secretion (IgG, IgM, IgA or secretory IgA classes) did not result in predictive values of greater than 32%. It is concluded that the detection of chlamydial antibodies in serum or cervical secretions cannot be substituted for agent isolation in diagnosing these infections.     

Solid-phase radioimmunoassay of serum immunoglobulin A antibodies to respiratory syncytial virus and adenovirus.

A solid-phase radioimmunoassay for detecting respiratory syncytial virus and adenovirus serum immunoglobulin A (IgA) antibodies was developed. An antigen consisting of purified adenovirus type 2 hexons or a crude lysate of respiratory syncytial virus-infected cells was first adsorbed onto polystyrene beads. The coated beads were then incubated with dilutions of serum, and IgA antibodies which attached to the solid-phase virus antigen were subsequently detected with 125I-labeled anti-human alpha antibodies. The anti-human alpha antibodies used were isolated by immunosorbent chromatography from rabbit antiserum produced by immunization with IgA purified from serum of an IgA myeloma patient. A total of 46 serum specimens from 13 patients with respiratory syncytial virus infections and 10 patients with adenovirus infections were tested. Complement fixation, homologous IgG and IgM radioimmunoassay, and heterologous IgA radioimmunoassay testing were also done. Specific values higher than 10,000 cpm were often reached with convalescent serum specimens, and positive-to-negative serum binding ratios of 50 or more were frequently obtained with lower serum dilutions. IgA titers of convalescent sera were from 1,000 to 16,000, and with few exceptions a fourfold or greater rise in the IgA titer was detected in the homologous IgA radioimmunoassay.     

Simultaneous detection of immunoglobulin A (IgA) and IgM antibodies against hepatitis E virus (HEV) Is highly specific for diagnosis of acute HEV infection

Serum samples collected from 68 patients (age, mean +/- the standard deviation [SD], 56.3 +/- 12.8 years) at admission who were subsequently molecularly diagnosed as having hepatitis E and from 2,781 individuals who were assumed not to have been recently infected with hepatitis E virus (HEV; negative controls; 52.9 +/- 18.9 years), were tested for immunoglobulin M (IgM) and IgA classes of antibodies to HEV (anti-HEV) by in-house solid-phase enzyme immunoassay with recombinant open reading frame 2 protein expressed in the pupae of silkworm as the antigen probe. The 68 patients with hepatitis E had both anti-HEV IgM and anti-HEV IgA. Among the 2,781 controls, 16 (0.6%) had anti-HEV IgM alone and 4 (0.1%) had anti-HEV IgA alone: these IgA/IgM anti-HEV-positive individuals were not only negative for HEV RNA but lack IgG anti-HEV antibody as well (at least in most of the cases). Periodic serum samples obtained from 15 patients with hepatitis E were tested for HEV RNA, anti-HEV IgM, and anti-HEV IgA. Although HEV RNA was detectable in the serum until 7 to 40 (21.4 +/- 9.7) days after disease onset, both IgM and IgA anti-HEV antibodies were detectable until 37, 55, or 62 days after disease onset in three patients and up through the end of the observation period (50 to 144 days) in 12 patients. These results indicate that detection of anti-HEV IgA alone or along with anti-HEV IgM is useful for serological diagnosis of hepatitis E with increased specificity and longer duration of positivity than that by RNA detection.     

Anti-alpha-galactosyl immunoglobulin A (IgA), IgG, and IgM in human secretions.

Anti-alpha-galactosyl (anti-Gal) is a natural human serum antibody that binds to the carbohydrate Gal alpha 1,3Gal beta 1,4GlcNAc-R (alpha-galactosyl epitope) and is synthesized by 1% of circulating B lymphocytes in response to immune stimulation by enteric bacteria. We were able to purify secretory anti-Gal from human colostrum and bile by affinity chromatography on silica-linked Gal alpha 1,3Gal beta 1,4GlcNAc. We found similar secretory anti-Gal antibodies in human milk, saliva, and vaginal washings. Secretory anti-Gal from milk and saliva was exclusively immunoglobulin A (IgA); that from colostrum and bile also contained IgG and IgM isotypes. Serum was also found to contain anti-Gal IgM and IgA in addition to the previously reported IgG. Anti-Gal IgA purified from colostrum and bile had both IgA1 and IgA2. Secretory anti-Gal from saliva, milk, colostrum, and bile agglutinated rabbit erythrocytes (RRBC) and bound to bovine thyroglobulin, both of which have abundant alpha-galactosyl epitopes. The RRBC-hemagglutinating capacity of human saliva, milk, bile, and serum was specifically adsorbed by immobilized Gal alpha 1,3Gal beta 1,4GlcNAc but not by Gal alpha 1,4Gal beta 1,4GlcNAc, Gal beta 1,3GalNAc, Gal beta 1,4GlcNAc, Gal beta 1,4GlcNAc alpha 1,2Man, or Fuc alpha 1,2Gal beta 1,4GlcNAc. No RRBC-hemagglutinating activity could be detected in rat milk, rat bile, cow milk, or rabbit bile, suggesting a restricted species distribution for secretory anti-Gal similar to that found for serum anti-Gal. Colostral anti-GaI IgA bound strongly to a sample of gram-negative bacteria isolated from the throats and stools of well children as well as to an Escherichia coli K-1 blood isolate. Colostral anti-GaI IgA inhibited the binding of a Neisseria meningitidis strain to human buccal epithelial cells, suggesting that this antibody may play a protective role at the mucosal surface.