Human gut mycobiota tune immunity via CARD9-dependent induction of anti-fungal IgG antibodies.

Antibodies mediate natural and vaccine-induced immunity against viral and bacterial pathogens, whereas fungi represent a widespread kingdom of pathogenic species for which neither vaccine nor neutralizing antibody therapies are clinically available. Here, using a multi-kingdom antibody profiling (multiKAP) approach, we explore the human antibody repertoires against gut commensal fungi (mycobiota). We identify species preferentially targeted by systemic antibodies in humans, with Candida albicans being the major inducer of antifungal immunoglobulin G (IgG). Fungal colonization of the gut induces germinal center (GC)-dependent B cell expansion in extraintestinal lymphoid tissues and generates systemic antibodies that confer protection against disseminated C. albicans or C. auris infection. Antifungal IgG production depends on the innate immunity regulator CARD9 and CARD9+CX3CR1+ macrophages. In individuals with invasive candidiasis, loss-of-function mutations in CARD9 are associated with impaired antifungal IgG responses. These results reveal an important role of gut commensal fungi in shaping the human antibody repertoire through CARD9-dependent induction of host-protective antifungal IgG.

Antibodies elicited in humans upon chimeric hemagglutinin-based influenza virus vaccination confer FcγR-dependent protection in vivo.

Antibody responses against highly conserved epitopes on the stalk domain of influenza virus hemagglutinin (HA) confer broad protection; however, such responses are limited. To effectively induce stalk-specific immunity against conserved HA epitopes, sequential immunization strategies have been developed based on chimeric HA (cHA) constructs featuring different head domains but the same stalk regions. Immunogenicity studies in small animal models, as well as in humans, revealed that cHA immunogens elicit stalk-specific IgG responses with broad specificity against heterologous influenza virus strains. However, the mechanisms by which these antibodies confer in vivo protection and the contribution of their Fc effector function remain unclear. To characterize the role of Fc-FcγR (Fcγ receptor) interactions to the in vivo protective activity of IgG antibodies elicited in participants in a phase I trial of a cHA vaccine candidate, we performed passive transfer studies of vaccine-elicited IgG antibodies in mice humanized for all classes of FcγRs, as well as in mice deficient for FcγRs. IgG antibodies elicited upon cHA vaccination completely protected FcγR humanized mice against lethal influenza virus challenge, while no protection was evident in FcγR-deficient mice, suggesting a major role for FcγR pathways in the protective function of vaccine-elicited IgG antibodies. These findings have important implications for influenza vaccine development, guiding the design of vaccination approaches with the capacity to elicit IgG responses with optimal Fc effector function.

Afucosylated IgG responses in humans - structural clues to the regulation of humoral immunity.

Healthy immune responses require efficient protection without excessive inflammation. Recent discoveries on the degree of fucosylation of a human N-linked glycan at a conserved site in the immunoglobulin IgG-Fc domain might add an additional regulatory layer to adaptive humoral immunity. Specifically, afucosylation of IgG-Fc enhances the interaction of IgG with FcγRIII and thereby its activity. Although plasma IgG is generally fucosylated, afucosylated IgG is raised in responses to enveloped viruses and Plasmodium falciparum proteins expressed on infected erythrocytes, as well as during alloimmune responses. Moreover, while afucosylation can exacerbate some infectious diseases (e.g., COVID-19), it also correlates with traits of protective immunity against malaria and HIV-1. Herein we discuss the implications of IgG afucosylation for health and disease, as well as for vaccination.

The Identification of Enteric Fever-Specific Antigens for Population-Based Serosurveillance.

BACKGROUND: Enteric fever, caused by Salmonella enterica serovars Typhi and Paratyphi A, is a major public health problem in low- and middle-income countries. Moderate sensitivity and scalability of current methods likely underestimate enteric fever burden. Determining the serological responses to organism-specific antigens may improve incidence measures. METHODS: Plasma samples were collected from blood culture-confirmed enteric fever patients, blood culture-negative febrile patients over the course of 3 months, and afebrile community controls. A panel of 17 Salmonella Typhi and Paratyphi A antigens was purified and used to determine antigen-specific antibody responses by indirect ELISAs. RESULTS: The antigen-specific longitudinal antibody responses were comparable between enteric fever patients, patients with blood culture-negative febrile controls, and afebrile community controls for most antigens. However, we found that IgG responses against STY1479 (YncE), STY1886 (CdtB), STY1498 (HlyE), and the serovar-specific O2 and O9 antigens were greatly elevated over a 3-month follow up period in S. Typhi/S. Paratyphi A patients compared to controls, suggesting seroconversion. CONCLUSIONS: We identified a set of antigens as good candidates to demonstrate enteric fever exposure. These targets can be used in combination to develop more sensitive and scalable approaches to enteric fever surveillance and generate invaluable epidemiological data for informing vaccine policies. CLINICAL TRIAL REGISTRATION: ISRCTN63006567.

Neonatal SARS-CoV-2 immunoglobulin G antibodies at delivery and their impact on COVID-19.

OBJECTIVE: To assess neonatal SARS-CoV-2 anti-spike IgG antibody levels after maternal mRNA COVID-19 vaccination and/or infection during pregnancy and evaluate their protective effect. METHODS: Prospective observational study, conducted from January 2021 to December 2022. Infants were tested for anti-spike IgG antibodies at birth and then every 3 months until disappearance of titer. A follow-up was done for SARS-CoV-2 infection up to 12 months. RESULTS: In total, 147 newborns were enrolled with a median (IQR) gestational age of 39.60 weeks (38.3-40.4). Median (IQR) titers in UA/ml at 2 days were higher (P < .001) in newborns of vaccinated 7063.7 (2841.4-14,448.1), than of infected mothers 372.7 (158.00-884.90). Titers dropped significantly during the follow-up but 50% still had a detectable titer at 6 months. A high antibody titer at 2 days led to a longer persistence (HR 0.89, IC 95% 0.83-0.96, P = .004). In total, 36 infants were infected during the first months of life coinciding with the Omicron variant. Fifty percent had detectable antibodies during the infection period. Relationship between high IgG titers and month of infection was inverse (RHO - 0.52, P = .009). CONCLUSION: Though a high antibody titer at birth led to longer persistence, no protective effect against infection was found. As newborns are a high risk group for COVID-19, avoiding transmission during the first year of life is important.

Determination of optimum levels of binding antibody units (BAU) of new quantitative chemiluminescent immuno-assay (CLIA) in COVID-19 vaccinated volunteer blood donors.

BACKGROUND: For assessment of COVID-19 vaccine efficacy, neutralization activity of anti-SARS-CoV-2 antibody is measured. This study was undertaken to determine optimum levels of binding antibody units (BAU/ml) in new quantitative chemiluminescent assay (CLIA) that corresponded to neutralizing potential (30% inhibition) of sVNT assay. METHODS: Ninety-one blood samples were analyzed by CLIA and sVNT assays. Test samples (n = 75) were collected from blood donors post-2nd vaccination dose, while control samples (n = 16) were archived pre-COVID donor samples. Correlation between CLIA and sVNT was calculated and receiver operating characteristic (ROC) curve was drawn and analyzed. RESULTS: Results indicated excellent correlation between 57.5 BAU/ml on CLIA and 30%inhibition on sVNT assay. ROC curve analysis revealed that the area under the curve (AUC) was 0.971. DISCUSSION: The present study determined that 57.5 BAU/ml on CLIA corresponded to 30% inhibition on sVNT assay. Periodic quantitative analysis.

The impact of existing total anti-toxin B IgG immunity in outcomes of recurrent Clostridioides difficile infection.

Late anti-toxin-B humoral immunity acquired after treatment is important for preventing recurrent Clostridioides difficile infection. We prospectively-measured anti-toxin-B IgG and neutralization titers at diagnosis as potential early predictors of recurrence. High anti-toxin-B-IgG/neutralizing antibodies were associated with short-lasting protection within 6-weeks, however, no difference in recurrence risk was observed by 90-days post-infection.

Experimental support for reclassification of the light scattering second virial coefficient from macromolecular solutions as a hydrodynamic parameter.

This investigation examines the source of the disparity between experimental values of the light scattering second virial coefficient [Formula: see text] (mL.mol/g2) for proteins and those predicted on the statistical mechanical basis of excluded volume. A much better theoretical description of published results for lysozyme is obtained by considering the experimental parameters to monitor the difference between the thermodynamic excluded volume term and its hydrodynamic counterpart. This involves a combination of parameters quantifying concentration dependence of the translational diffusion coefficient obtained from dynamic light scattering measurements. That finding is shown to account for observations of a strong correlation between [Formula: see text] (mL/g), where M2 is the molar mass (molecular weight) of the macromolecule and the diffusion concentration parameter [Formula: see text] (mL/g). On the grounds that [Formula: see text] is regarded as a hydrodynamic parameter, the same status should be accorded the light scattering second virial coefficient rather than its current incorrect thermodynamic designation as [Formula: see text] (mL.mol/g2), or just B, the osmotic second virial coefficient for protein self-interaction.

Seroprevalence of SARS-CoV-2 antibodies in Italy in newborn dried blood spots.

OBEJCTIVES: Serosurveys can be used to monitor COVID-19 seroprevalence and conduct surveillance. Dried blood spot (DBS), used increasingly as a valuable sample to assay severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) antibodies (Ab), has several advantages, particularly in infants, due to the limited amount of blood required and its utility in testing a large number of samples in a limited time-frame. We evaluated SARS-CoV-2 IgG Ab prevalence in newborn DBS in the Trentino region of Italy, during the time period January 2020 - December 2021. METHODS: Anti-SARS-CoV-2 IgG levels were determined in DBS by means of Anti-SARS-CoV-2 QuantiVac IgG ELISA assay (Euroimmun, Lubeck, Germany). RESULTS: Analyses included 2,400 DBS from newborns (54% M, 46% F), samples being collected 2-3 days after birth. The first DBS that tested positive for anti-SARS-CoV-2 IgG antibodies was found in March 2020 and, up to May 2020, only 4 positive results were detected overall. Starting from June 2020, the positivity thresholds increased according to the epidemiological waves of the COVID-19 pandemic in Italy, with a robust increment in the winters of 2020 and 2021. The percentage of positive DBS rose from 0 to 6% to 10-47%, in 2020 and 2021, respectively. CONCLUSIONS: This study demonstrates DBS is a suitable tool for both epidemiological purposes and surveillance in the SARS-CoV-2 pandemic, particularly in newborns and pregnant women, saving blood waste and sparing patients any discomfort.

Cost-effectiveness analysis of diagnostic strategies for COVID-19 in Iran.

BACKGROUND: Since 2020, COVID-19 has become a global public health issue and has caused problems worldwide. This infection can lead to a fever and respiratory problems. Asymptomatic carriers of the virus are a significant part of the spread of the disease, so early screening and diagnosis of suspected cases of COVID-19 are essential. Generally, standard diagnostic methods include lung imaging (CT), polymerase chain reaction (PCR), and corona antibody (IgM&IgG) testing. However, the costs of the above tests for the healthcare system cannot be ignored, and evaluating the incremental costs against the additional benefit is necessary. Therefore, this study aimed to determine the cost-effectiveness of diagnostic methods for COVID-19 patients. MATERIALS AND METHODS: In this research, an economic evaluation analysis was conducted to reveal the cost-effectiveness of the diagnostic strategies for COVID-19 from the service provider's perspective. Basic information about the costs of CT, serology (IgG&IgM), and molecular (PCR) tests were collected from the Ministry of Health of Iran. The effectiveness data were calculated according to the sensitivity and specificity of the diagnostic tests for COVID-19. In this study, the incremental cost-effectiveness ratio (ICER) of the diagnostic strategies for COVID-19 was estimated, and the most cost-effective diagnostic strategy was determined. In calculating ICER and analyzing the sensitivity of the results, Treeage software was used. RESULTS: According to the calculated incremental effectiveness cost ratio for scenarios with 5, 10, and 50% prevalence of COVID-19 and according to the threshold defined by the World Health Organization, in the study, PCR, PCR, and IgG&IgM strategies are the most cost-effective diagnostic methods of the corona. Also, the results were not sensitive to the desired parameters based on the results of one-way sensitivity analysis. CONCLUSION: Nowadays there are various tests with different levels of accuracy in the diagnosis of COVID-19. In general, PCR tests are more cost-effective for low prevalence of Covid-19, while IgM&IgG tests are more cost-effective for high estimated prevalence. The results of this research can help policymakers and health system managers to validate the most accurate diagnostic method for COVID-19, considering the prevalence of the disease.

SARS-CoV-2 Spike Protein and Neutralizing Anti-Spike Protein Antibodies Modulate Blood Platelet Function.

Several studies report elevated blood platelet activation and altered platelet count in COVID-19 patients, but the role of the SARS-CoV-2 spike protein in this process remains intriguing. Additionally, there is no data that anti-SARS-CoV-2 neutralizing antibodies (nAb) may attenuate spike protein activity toward blood platelets. Our results indicate that under in vitro conditions, the spike protein increased the collagen-stimulated aggregation of isolated platelets and induced the binding of vWF to platelets in ristocetin-treated blood. The spike protein also significantly reduced collagen- or ADP-induced aggregation or decreased GPIIbIIIa (fibrinogen receptor) activation in whole blood, depending on the presence of the anti-spike protein nAb. Our findings suggest that studies on platelet activation/reactivity in COVID-19 patients or in donors vaccinated with anti-SARS-CoV-2 and/or previously-infected COVID-19 should be supported by measurements of spike protein and IgG anti-spike protein antibody concentrations in blood.

Human papillomavirus-specific antibody status among unvaccinated subjects in the region of Vojvodina, Serbia.

OBJECTIVES: The aim of the study was to evaluate the immune status of young people from the Vojvodina province, Serbia, through the detection of IgG antibodies specific for the L1 protein of HPV types 6, 11, 16, and 18 contained in quadrivalent vaccine. METHODS: The study enrolled 514 healthy persons of both genders, aged between 18 and 30 years. All potential participants were informed about the project's aims by trained interviewers before venous blood collection. Also, participants completed a specially designed anonymous questionnaire to identify socio-demographic characteristics and individual behaviours associated with HPV seroprevalence. VPL HPV L1-specific IgG antibodies were measured using a semi-quantitative HPV IgG ELISA kit (Dia.Pro, Italy). RESULTS: A total of 472 (91.8%) young subjects had no detectable antibodies against high- and low-risk HPV types covered by the quadrivalent vaccine. A slightly higher number of seropositive individuals were detected in the age group of 26-30 years compared to younger than 25. Multivariate analysis showed that the number of lifetime sexual partners was the most powerful predictor of HPV seropositivity (OR = 3.483, 95% CI: 1.294-9.379). CONCLUSIONS: Obtained data point out low levels of naturally induced HPV-specific serum antibodies among the target population in the Vojvodina province. The present work highlights the significance and potential benefits of HPV vaccination. Routine HPV vaccination should be the public health priority in our country and should be included in the national immunization programme as soon as possible.

Prevalence of JC Polyomavirus in Patients with Neuroinvasive Disease of Unknown Etiology in Croatia.

Background and Objectives: John Cunningham polyomavirus (JCPyV) is a highly prevalent virus in the human population. The prevalence of JCPyV in patients with central nervous system disorders has not been examined extensively. The aim of this study was to analyze the prevalence of JCPyV DNA/antibodies in patients with neuroinvasive diseases (NID) of unknown etiology. Materials and Methods: The study included 132 patients with NID (febrile headache, meningitis, encephalitis) tested from January 2021 to December 2022. The control group consisted of 47 asymptomatic individuals. In patients with NID, serum and cerebrospinal fluid (CSF) samples were collected in the acute phase of the disease. CSF samples were tested for JCPyV DNA (PCR), while serum samples were tested for JCPyV IgG antibodies (ELISA). In controls, serum samples were tested for JCPyV IgG antibodies (ELISA). Results: JCPyV DNA was not detected in any of the CSF samples from patients with NID. JCPyV IgG antibodies were detected in 88.6% of patients and 74.5% of controls (p < 0.001). In the patients' group, a significant difference in the IgG prevalence was observed between males (94.6%) and females (81.0%). In addition, significant differences in the seropositivity between age groups were found. The lowest seroprevalence (28.6%) was in patients less than 20 years, followed by a sharp increase in the 20-29-year group (69.2%), after which the seroprevalence remained stable (90.0-94.1%) in patients up to 69 years. All patients older than 70 years were JCPyV IgG-seropositive. No significant difference in the seroprevalence was found in patients presenting with febrile headache (81.6%), meningitis (93.3%), or meningoencephalitis (91.3%). No difference in the seropositivity between genders was found in controls. Although the seropositivity steadily increased in older participants, these differences were not significant. Analyzing the JCPyV antibody levels in patients with NID, the median antibody titers differed significantly between groups, ranging from 248 AU/mL (younger age groups) to 400 AU/mL (older age groups). Conclusions: Higher seroprevalence in the patients' group highlights the need to further investigate the possible association of JCPyV and NID.

Seroprevalance of anti-SARS-CoV-2 antibodies in the IgG class in hospitalized children in the north-eastern part of Poland in 2021.

Introduction: In children, SARS-CoV-2 infection may manifest with symptoms of fever, cough, muscle pain, diarrhea or waste smell and taste. However, in most cases it is mild or asymptomatic. Determination of the level of anti-SARS CoV-2 IgG antibodies in children enables to assess retrospectively the incidence of the SARS-CoV-2 infection among children. Aim of the study: The aim of the research was to analyze the results of anti-SARS-CoV-2 antibodies in the IgG class contained in children hospitalized in north-eastern Poland in 2021. Material and methods: The material for the study was venous blood collected once from children hospitalized in Children's University Hospital in Bialystok in 2021. The results obtained from 615 children aged from 1 month to 11 years were analyzed. Determination of the level of antibodies was performed using the automated SARS-COV-2 IgG II test on the VIDAS® analyzer. Results: The analysis of the results of the anti-SARS-CoV-2 IgG value showed that half of children (52%, n=319) had contact with SARS-CoV-2 virus of which approximately 15% (n=47) had documented infection with this virus. There was no difference in the frequency of infections among boys and girls, antibodies were detected in 51% and 53%, respectively. The highest percentage of positive results was observed in children aged 7 to 10 years, 62% (91/147). The least children with a positive result were in the group below 1 year of age, 24% (4/17). High values of the antibody index (>15.00) were most often found among younger children, aged 1-2 years. Conclusions: The presented results showed that infection with the SARS-CoV-2 virus does not depend on the sex of children but the value of anti-SARS-CoV-2 IgG antibodies decreased with the age of the child.

Breakthrough COVID-19 infections - Analyzing our experience.

Objective: There are many cases of post-vaccination COVID-19 globally. Also, literature on serum antibodies after vaccination is abundant. Our research focuses on breakthrough infections reported at our institution during the third wave of COVID-19. Methods: A total of 177 people recruited at the Indus Hospital Karachi between May to September 2021 with COVID-19 infection were divided into vaccinated, partially vaccinated, and unvaccinated cohorts. Furthermore, a subset of the vaccinated cohort was tested for anti-NP and anti-S antibodies. Results: There were 119 patients with breakthrough infection, however, 74% had mild symptoms. The antibodies against NP and S were found at a higher level in those who had a breakthrough infection in comparison to healthy vaccinated controls. Conclusion: Vaccination does not prevent disease but does confer some immunity causing less severe infection.

Persistence of neutralizing antibodies a year after SARS-CoV-2 infection in humans.

Most subjects develop antibodies to SARS-CoV-2 following infection. In order to estimate the duration of immunity induced by SARS-CoV-2 it is important to understand for how long antibodies persist after infection in humans. Here, we assessed the persistence of serum antibodies following WT SARS-CoV-2 infection at 8 and 13 months after diagnosis in 367 individuals. The SARS-CoV-2 spike IgG (S-IgG) and nucleoprotein IgG (N-IgG) concentrations and the proportion of subjects with neutralizing antibodies (NAb) were assessed. Moreover, the NAb titers among a smaller subset of participants (n = 78) against a WT virus (B) and variants of concern (VOCs): Alpha (B.1.1.7), Beta (B.1.351), and Delta (B.1.617.2) were determined. We found that NAb against the WT virus persisted in 89% and S-IgG in 97% of subjects for at least 13 months after infection. Only 36% had N-IgG by 13 months. The mean S-IgG concentrations declined from 8 to 13 months by less than one third; N-IgG concentrations declined by two-thirds. Subjects with severe infection had markedly higher IgG and NAb levels and are expected to remain seropositive for longer. Significantly lower NAb titers against the variants compared to the WT virus, especially after a mild disease, suggests reduced protection against VOCs.

Improved immunologic response to COVID-19 vaccine with prolonged dosing interval in haemodialysis patients.

Vaccination against 2019 coronavirus disease (COVID-19) can reduce disease incidence and severity. Dialysis patients demonstrate a delayed immunologic response to vaccines. We determined factors affecting the immunologic response to COVID-19 vaccines in haemodialysis patients. All patients within a Swedish haemodialysis network, vaccinated with two doses of COVID-19 vaccine 2-8 weeks before inclusion, were eligible for this cross-sectional study. Severe adult respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein antibody levels were determined by EliA SARS-CoV-2-Sp1 IgG test (Thermo Fisher Scientific, Phadia AB) and related to clinical and demographic parameters. Eighty-nine patients were included. Patients were vaccinated with two doses of Comirnaty (BNT162b2, 73%) or Spikevax (mRNA-1273, 23,6%). Three patients received combinations of different vaccines. Response rate (antibody titres >7 U/mL) was 89.9%, while 39.3% developed high antibody titres (>204 U/mL), 47 (43-50) days after the second dose. A previous COVID-19 infection associated with higher antibody titres (median (25th-75th percentile) 1558.5 (814.5-3,763.8) U/mL vs 87 (26-268) U/mL, P = .002), while time between vaccine doses did not differ between groups (P = .7). Increasing SARS-CoV-2 antibody titres were independently associated with increasing time between vaccine doses (B 0.241, P = .02), decreasing serum calcium levels (B -0.233, P = .007) and previous COVID-19 (B 1.078, P < .001). In conclusion, a longer interval between COVID-19 mRNA vaccine doses, lower calcium and a previous COVID-19 infection were independently associated with a stronger immunologic vaccination response in haemodialysis patients. While the response rate was good, only a minority developed high antibody titres, 47 (43-50) days after the second vaccine dose.

Dynamics of the Immune Response in Hospitalized SARS-CoV-2-infected Cancer Patients.

Seroconversion rates were compared between oncological and nononcological patients infected with SARS-CoV-2 during a 14-day hospitalization time. All COVID-19 non-oncological and solid malignancies patients reached 100% seroconversion at day 14, while less than half of the hematological patients were seroconverted at the same time point. Despite the limited number and variability of the patient's cohort, we conclude that there is a delayed seroconversion in the hematological malignancies group, which may be linked to changes in the hematological parameters, immune suppression and/or oncological treatments that are typically associated with these patients.

ELISA-based evaluation of antibody response to Leishmania in a region endemic for cutaneous leishmaniasis.

Leishmaniasis includes several clinical forms. While routine diagnosis of cutaneous leishmaniasis (CL) is by microscopy, an antibody response to CL has been reported in several recent studies. This study evaluated anti-leishmanial immunoglobulin G (IgG) antibody responses as a biomarker of active leishmaniasis and a measure of exposure to Leishmania. Sera from 50 untreated CL patients, 140 patients under treatment and 280 healthy individuals residing in endemic regions collected as part of an epidemiological survey, was analysed with an enzyme-linked immunosorbent assay established in-house using receiver operator characteristic curve at optimized cut-off value. The assay showed high performance as a diagnostic tool in identifying exposure in endemic individuals (sensitivity: 98%, specificity: 90.3%). All patients showed lower antibody levels over time since onset of lesion/s. Antibody levels were higher (p Ë‚ .01) and persisted for a longer period in untreated patients. In patients under treatment, the level of anti-IgG antibodies was negatively correlated with the total duration the patient had been on treatment. The anti-leishmanial IgG response in Leishmania donovani-induced CL is transient and is unlikely to confer protective immunity. Optimized serological assays may be useful in endemic settings for diagnosis and monitoring the treatment response in CL.

Breast milk contains red cell isohaemagglutinins: An observational study of 176 mothers.

BACKGROUND AND OBJECTIVES: Maternal antibodies are transferred to the child, predominantly IgG, via the transplacental route, and mostly IgA through breast milk. Cases reported by us and others have shown the transfer of red cell allo-antibodies through breast milk. This study was conducted to assess the presence of isohaemagglutinins in breast milk, the range of titres, and the correlation between breast milk and maternal plasma titres. MATERIALS AND METHODS: A total of 176 mothers were recruited in this study. Breast milk was collected after sufficient feeding was established and within 2-5 days of delivery in a sterile container without any anticoagulant. Antibody screen, identification and titres were performed on maternal plasma as well as breast milk. RESULTS: Anti-A and anti-B in breast milk corresponding to their respective maternal blood groups were found in all the samples. This study has shown titres in the breast milk of anti-A and anti-B ranging from 2 to 1024 in both saline and Coombs phases. There was no association between plasma and breast milk titres, thus making it impossible to predict which mother may potentially transfer a larger amount of these haemagglutinins. Isotypes of anti-A and anti-B were evaluated in both plasma and breast milk of 11 samples, which showed predominantly IgG in 7 (63.63%) and predominantly IgA in 4 (36.36%) samples. CONCLUSION: Our study demonstrates the presence of a wide range of titres for IgG antibodies of the ABO blood group system in breast milk. The clinical impact of this finding needs to be studied further, as it assumes great relevance in developing countries where anaemia continues to challenge young infants.