SUMMARY: Naturally occurring anti-ABO(H) antibodies represent the most common barrier to transfusion and transplantation. These antibodies can vary wildly in titer and specificity, resulting in distinct clinical outcomes following ABO(H) incompatibility. Formation of these antibodies is linked directly to host interaction with specific microbial strains that express blood group positive carbohydrate antigens. The overarching goal of Core B is to provide tools for assessment of the role of microbial populations in driving and shaping naturally occurring anti- blood group antibody responses and their clinical consequences. To this end we will provide microbial microarrays for the high throughput analysis of both innate and adaptive immune interactions with a wide array of microbial glycans. Our recent discoveries that innate and adaptive immune factors interact with a variety of distinct microbial glycans using a platform populated with microbial glycans isolated and printed in a microarray format have already demonstrated the utility of this approach in elucidating key host-microbe interactions. These results recapitulate actual interactions with intact microbes. As microbial communities are numerous and diverse, our preliminary data also importantly demonstrate that specific microbes expressing blood group antigen can be specifically isolated from a complex microbial mixture and that microbial glycans from these microbes can be similarly isolated, printed and interrogated for host immune factor interactions, allowing a triage approach for printing of relevant microbes. While these preliminary data demonstrate the feasibility and utility of this approach, most microbes that express blood group antigens are not yet represented on currently formats. As a result, to provide the breadth of microbial coverage needed to effectively assess host microbial interactions related to development of anti-ABO(H) antibodies and therefore directly facilitate the studies outlined in each Project of the program project grant (PPG) program, we propose the following specific aims: Aim 1: Continue to generate validated microarrays populated with blood group positive and negative intact microbes and their corresponding microbial glycans. In this aim we will continue to make existing microbial microarray platforms available to each Project, through the continued printing of these platforms that contain previously isolated blood group positive and negative microbes. Each array platform will be validated prior to use to facilitate reproducibility and data comparison across the entire PPG. Aim 2: Culture, characterize and isolate glycans from newly identified blood group positive and negative microbes for incorporation into expanded microbial array platforms. In this aim we will expand existing microbial microarrays by incorporating microbial glycans and corresponding intact microbes isolated by the various Projects throughout the course of the proposed studies into array p...