Molecular Analysis Of Leukocyte Activation By Chemoattractants

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications & trials

Abstract

The aim of this project is to define the molecular mechanisms and biological contexts for blood leukocyte migration to specific tissue sites that are inflamed or infected. We have focused on chemoattractant proteins that mediate this process and have identified members of a large family of chemoattractant receptors that are deployed on the leukocyte cell surface. We have also identified members of a diverse group of chemoattractant and chemoattractant receptor mimics made by viruses, including herpesviruses, poxviruses and HIV. We use genomics, molecular biology, cell biology and epidemiology as the principle methods for analyzing these molecules. A major goal is to identify specific disease associations of individual chemoattractants and chemoattractant receptors, in order to identify potential new therapeutic targets. A key strategy is to analyze phenotypes of gene knockout mice in disease models as well as phenotypes in patients with mutations in human chemoattractant system genes. 1.) In FY21, we reported a case series of neonates born to patients with WHIM syndrome immunodeficiency, who inherited the disease-causing mutation and tested positive for low TRECs by newborn SCID screening. This study was a follow up of our FY20 case report of low TREC in a WHIM neonate. The validation in this case series suggests the possibility that univeral newborn screening for SCID may be leveraged to accelerate detection, diagnosis and effective management of children with de novo WHIM mutations. Thus, there is the immediate potential to change medical practice for the benefit of these rare patients. 2.) In FY21, we reported in a collaborative study a new immunodeficiency disease named SASH3 deficiency. The study emerged from the discovery of damaging mutations in four NIAID immunodeficiency patients. Three patients were SASH3 protein negative whereas our patient was protein positive. Our patient presented with clinical findings strongly overlapping those found in patients with WHIM syndrome, a disease our section has studied intensely for 16 years. However, he did not have a mutation in the WHIM gene CXCR4. The biochemical function of SASH3 remains unknown; however, all four patients presented with severe acute and chronic infections including HPV and polyomavirus infections associated with defects in both innate and adaptive immunity. This study motivates further investigation of SASH3 function and provides a direction for gene therapy in the patients. 3.) In FY21, we reported chromoanasynthesis as a cause of Jacobsen Syndrome. This research continues our interest in complex chromosomal rearrangements in genomic disorders, begun by our characterization of patient WHIM-09, who was cured of WHIM syndrome immunodeficiency by chromothripsis, an acquired complex chromosomal rearrangement in which 164 genes were deleted, including the disease-causing gene, in a single hematopoietic stem cell, which thereby acquired a selective growth advantage, outcompeting WHIM HSCs, resulting in non-WHIM myelopoiesis, correction of mature myeloid deficiency and resolution of clinical manifestations durable for over 25 years, i.e. cure. In this second case, we reported a patient with a congenital form of complex chromosomal rearrangement distinct from chromothripsis known as chromoanasynthesis. This boy presented at birth with developmental defects including craniofacial dysmorphism, and delayed motor and language development. We defined the chromoanasynthetic event by whole genome sequencing, microarray analysis and cytogenetics as multiple gene deletions and duplications on chromosome 11q, including deletions in the terminal portion of 11q. As such, the patient met the criteria for the 11q deletion syndrome, also known as Jacobsen syndrome, which is characterized by most of the phenotypes present in the patient as well as several others. This is one of a small number of cases of congenital chromoanasynthesis that have been published, and one of the only ones to cause a recognized genomic syndrome. A major point of the paper is that cytogenetic analysis is insufficient to reveal the full array of defects in this patient, and that full understanding of the morbid genome in such cases really requires all three genomic modalities to be used. The sequence analysis at the breakpoint junctions in 11q revealed evidence consistent with a replication based mechanism of chromosomal damage and rearrangement concordant with a favored model of microhomology-mediated break induced repair. 4.) In FY21, we reported that mice lacking the phagocyte chemotactic receptor Fpr1 develop severe subcapsular cataracts as they age. The study represents a serendipitous finding of an unexpected non-hematopoietic phenotype of Fpr1 deficiency. The mechanism appears to involve effects of Fpr1 on lens epithelial cell apoptosis. The study highlights the multitasking capacity of Fpr1. 5. In FY21, we reported the detailed characterization of Ccr1l1 as a Rodentia-restricted eosinophil-selective chemokine receptor homologue. Ccr1l1 is highly related to both Ccr1 and Ccr3, which together have over a dozen ligands, several of them shared, yet Ccr1l1 does not bind any of these and is not a pseudogene. A Ccr1l1 knockout mouse had not overt phenotypes. This places Ccr1l1 as an extreme outlier in the chemokine receptor family, in which receptors typically have multiple chemokine ligands including ones that are shared with related receptors. 6. In FY21, we reported a fundamental new discovery in chemokine biology, the widely shared ability of chemokines to bind not just to G protein-coupled receptors for leukocyte chemotactic signaling and glycosaminoglycans for storage, but also to specific membrane anionic phospholipids. The paper focuses on one such anionic phospholipid, phosphatidylserine (PS), which is a major factor involved in apoptotic cell clearance and demonstrates that PS-binding of chemokines is a specific property of apoptotic cells that mediates detection by macrophages. Thus, the finding describes this new binding interaction as a potentially general chemokine-dependent mechanism of apoptotic cell clearance, a fundamental process in biology. The section also contributed to multiple collaborative papers in the area of basic immunology focused on understanding the role of CXCR4 in homeostasis and disease.