L-plastin associated syndrome of immune deficiency and haematological cytopenia (PASIC).

BACKGROUND: LCP1 encodes L-plastin, an actin-bundling protein primarily expressed in hematopoietic cells. In mouse and fish models, LCP1 deficiency has been shown to result in hematological and immune defects. OBJECTIVE: To determine the nature of a human inborn error of immunity resulting from a novel genetic variant of LCP1. METHODS: We performed genetic, protein and cellular analysis of PBMCs from a kindred with apparent autosomal dominant immune deficiency. We identified a candidate causal mutation in LCP1, which we evaluated by engineering the orthologous mutation in mice and Jurkat cells. RESULTS: A splice-site variant in LCP1 segregated with lymphopenia, neutropenia, and thrombocytopenia. The splicing defect results in at least two aberrant transcripts, producing an in-frame deletion of 24 nucleotides, and a frameshifting deletion of exon 8. Cellular analysis of the kindred revealed a proportionate reduction of T and B cells, and a mild expansion of transitional B cells. Similarly, mice carrying the orthologous genetic variant exhibited the same in-frame aberrant transcript, reduced expression Lcp1 and gene dose-dependent leukopenia, mild thrombocytopenia, and lymphopenia, with a significant reduction of T cell populations. Functional analysis revealed that LCP1c740-1G>A confers a defect in platelet development and function with aberrant spreading on collagen. Immunological analysis revealed defective actin organisation in T cells, reduced migration of PBMCs from patients, splenocytes from mutant mice, and a mutant Jurkat cell line in response to CXCL12, impaired germinal centre B cell expansion after immunisation, and reduced cytokinesis during T cell proliferation. CONCLUSION: We describe a unique human hematopoietic defect affecting neutrophils, lymphocytes and platelets, arising from partial LCP1 deficiency.

DOCK2-deficiency causes defects in anti-viral T cell responses and impaired control of herpes simplex virus infection.

The expanding number of rare immunodeficiency syndromes offers an opportunity to understand key genes that support immune defence against infectious diseases. However, analysis of these in patients is complicated by their treatments and co-morbid infections requiring the use of mouse models for detailed investigations. Here we develop a mouse model of DOCK2 immunodeficiency and demonstrate that these mice have delayed clearance of herpes simplex virus type 1 (HSV-1) infections. We also uncovered a critical, cell intrinsic role of DOCK2 in the priming of anti-viral CD8+ T cells and in particular their initial expansion, despite apparently normal early activation of these cells. When this defect was overcome by priming in vitro, DOCK2-deficient CD8+ T cells were surprisingly protective against HSV-1-disease, albeit not as effectively as wild type cells. These results shed light on a cellular deficiency that is likely to impact anti-viral immunity in DOCK2-deficient patients.

Rare SH2B3 coding variants in lupus patients impair B cell tolerance and predispose to autoimmunity.

Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disease with a clear genetic component. While most SLE patients carry rare gene variants in lupus risk genes, little is known about their contribution to disease pathogenesis. Amongst them, SH2B3-a negative regulator of cytokine and growth factor receptor signaling-harbors rare coding variants in over 5% of SLE patients. Here, we show that unlike the variant found exclusively in healthy controls, SH2B3 rare variants found in lupus patients are predominantly hypomorphic alleles, failing to suppress IFNGR signaling via JAK2-STAT1. The generation of two mouse lines carrying patients' variants revealed that SH2B3 is important in limiting the number of immature and transitional B cells. Furthermore, hypomorphic SH2B3 was shown to impair the negative selection of immature/transitional self-reactive B cells and accelerate autoimmunity in sensitized mice, at least in part due to increased IL-4R signaling and BAFF-R expression. This work identifies a previously unappreciated role for SH2B3 in human B cell tolerance and lupus risk.

Zeb2 drives the formation of CD11c+ atypical B cells to sustain germinal centers that control persistent infection.

CD11c+ atypical B cells (ABCs) are an alternative memory B cell lineage associated with immunization, infection, and autoimmunity. However, the factors that drive the transcriptional program of ABCs have not been identified, and the function of this population remains incompletely understood. Here, we identified candidate transcription factors associated with the ABC population based on a human tonsillar B cell single-cell dataset. We identified CD11c+ B cells in mice with a similar transcriptomic signature to human ABCs, and using an optimized CRISPR-Cas9 knockdown screen, we observed that loss of zinc finger E-box binding homeobox 2 (Zeb2) impaired ABC formation. Furthermore, ZEB2 haplo-insufficient Mowat-Wilson syndrome (MWS) patients have decreased circulating ABCs in the blood. In Cd23Cre/+Zeb2fl/fl mice with impaired ABC formation, ABCs were dispensable for efficient humoral responses after Plasmodium sporozoite immunization but were required to control recrudescent blood-stage malaria. Immune phenotyping revealed that ABCs drive optimal T follicular helper (TFH) cell formation and germinal center (GC) responses and they reside at the red/white pulp border, likely permitting better access to pathogen antigens for presentation. Collectively, our study shows that ABC formation is dependent on Zeb2, and these cells can limit recrudescent infection by sustaining GC reactions.