Blood Group A Enhances SARS-CoV-2 Infection

BACKGROUND: Severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) continues to infect millions of individuals worldwide. However, not all individuals are equally susceptible to infection. Many studies have demonstrated that the first polymorphism described in the human population, ABO(H) blood group antigens, are associated with increased risk of SARS-CoV-2 infection. While conflicting data exist, the most common findings suggest that individuals with blood group A exhibit an increased risk of infection when compared to blood group O individuals. However, the mechanism whereby ABO(H) blood group status influences SARS-CoV-2 infection has remained unknown. The receptor binding domain (RBD) of SARS-CoV-2, which facilitates host cell engagement, bears significant similarity to galectins, an ancient family of carbohydrate binding proteins previously shown to recognize ABO(H) blood group antigens. As a result, we hypothesized that SARS-CoV-2 may recognize blood group A directly through its RBD and that this may in part account for increased susceptibility of blood group A individuals for SARS-CoV-2 infection.

Methods: The SARS-CoV-2 RBD from the parent strain (Wuhan-Hu-1) and variants (Delta and Omicron), in addition to individual human galectins (1, 2, 3, 4, 7 and 9) were cloned, purified and subjected to glycan binding specificity analysis using a glycan microarray populated with hundreds of distinct glycans, including blood group antigens. This was accomplished by incubating each fluorescently labeled RBD or galectin on the array, followed by detection of bound fluorescence using a microarray scanner (GenePix 4000 B, Molecular devices) and integrated spot intensity analysis using Imagene software (GenePix Pro 7). SARS-CoV-2 with distinct spike proteins (Wuhan-Hu-1, Delta, and Omicron) were used to assess infection using Chinese hamster ovary (CHO) cells engineered to express angiotensin converting enzyme 2 (ACE2) and type 1 blood group A or H (blood group O antigen). A one-way ANOVA with a Tukey's post hoc with a p value <0.05 was considered significant.

Results: Sequence analysis of galectins demonstrates that several galectins possess up to 11% sequence identity with the RBDs of SARS-CoV-2 WT (Wuhan-Hu-1) and variants (Delta and Omicron). Each RBD (Wuhan, Delta and Omicron) exhibited glycan binding specificity that overlapped with distinct members of the galectin family, with the highest similarity observed toward the C terminal domain of galectin-4 (Gal-4C). Direct comparison of binding toward ABO(H) antigens demonstrated that each RBD and Gal-4C displayed high specificity for the type 1 blood group A structure uniquely found on respiratory epithelial cells when compared to other blood group antigens (p<0.0001). To specifically examine the impact of blood group A on SARS-CoV-2 infection, CHO cells were engineered to express ACE2 and the type 1 blood group A or H antigen (the antigen expressed in blood group O individuals) normally found on respiratory epithelial cells. Consistent with the increased binding of the RBD to blood group A on the glycan microarray, enhanced binding was observed by each RBD toward blood group A expressing cells (p<0.001). Blood group A cells were also significantly more likely to be infected with Wuhan-Hu-1, Delta and Omicron variants of SARS-CoV-2 when compared to blood group O cells, while pre-incubation of cells with Gal-4C specifically inhibited infection of blood group A expressing cells, while failing to impact infection of blood group O cells (p<0.001).

Conclusions: These results demonstrate a direct effect of blood group A on viral infection and suggest that blood group A individuals may exhibit an increased susceptibility to SARS-CoV-2 as a result of direct engagement of the blood group A antigen. However, variations in ACE2 levels, blood group A expression and many other factors likely influence the overall risk of SARS-CoV-2 infection following exposure in a given individual. The present results provide one mechanism whereby blood group A itself may directly influence SARS-CoV-2 infectious risk.

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