All ETDs from UAB

Advisory Committee Chair

Daniel C Bullard

Advisory Committee Members

Susan L Bellis

Dennis F Kucik

Alexander J Szalai

Laura Timares

Document Type

Dissertation

Date of Award

2018

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Mac-1 (CD11b/CD18, ITGAM/ITGB2, CR3) is a member of the β2 integrin family. While primarily expressed on myeloid lineage cells such as monocyte/macrophages, neutrophils, and dendritic cells, Mac-1 is also found on natural killer cells and some B cells and T cell populations. Mac-1 has over 50 ligands, many of which are critical for adhesion, signaling, and the promotion of immune functions like phagocytosis. Genome-wide association studies (GWAS) have linked several SNPs in ITGAM, the gene which codes for CD11b, with the autoimmune disease systemic lupus erythematosus (SLE). rs1143679 results in an arginine to histidine change at amino acid position 77 (77His) in the β-propeller domain of CD11b and leads to impaired leukocyte adhesion to various ligands, altered cytokine generation, and decreased phagocytosis of iC3b opsonized particles. rs1143678 results in a proline to serine change at amino acid position 1146 (1146Ser) in the cytoplasmic tail of CD11b that also results in defects in leukocyte adhesion and phagocytosis. These SNPs are in high linkage disequilibrium, making it difficult to determine the effects each SNP have on Mac-1 functions. Furthermore, in vivo studies of these SNP variants are lacking. Therefore, my dissertation studies were designed to address the following questions: What is the impact of the 77His variant on Mac-1-mediated functions in vivo and how does 1146Ser affect Mac-1 activity? For our initial investigations, we generated a novel line of mice expressing the 77His CD11b variant. Analyses of these mice showed that this amino acid substitution did not result in any defects in myeloid cell recruitment or activation. Surprisingly, we demonstrated that 77His mice showed impaired antigen-specific T cell proliferation in vivo as well as in vitro using splenic dendritic cells. In other experiments, we performed a unique analysis of the protein structure and phosphorylation state of the cytoplasmic tail of 1146Ser CD11b. Our findings indicate that this amino acid substitution may result in a change in tertiary protein structure as well as generate additional kinase recognition motifs. Finally, studies using phospho-specific antibodies strongly suggested that the 1146Ser residue was phosphorylated in myeloid cells after stimulation.

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