Receptor Interacting Protein Kinase Pathways Regulate Innate B Cell Developmental Checkpoints But Not Effector Function in Mice.

Thomas Hägglöf,Elizabeth A Dudley,Alexandra Mclennan,Lily Q Dong,Abigail Kumagai,Elizabeth A Leadbetter,Raksha Parthasarathy,Aiden Mattke,Jason T Hadley

doi:10.3389/fimmu.2021.758407

Abstract

Mutations in the scaffolding domain of Receptor Interacting Protein kinases (RIP) underlie the recently described human autoimmune syndrome, CRIA, characterized by lymphadenopathy, splenomegaly, and autoantibody production. While disease mechanisms for CRIA remain undescribed, RIP kinases work together with caspase-8 to regulate cell death, which is critical for normal differentiation of many cell types. Here, we describe a key role for RIP1 in facilitating innate B cell differentiation and subsequent activation. By comparing RIP1, RIP3, and caspase-8 triple deficient and RIP3, caspase-8 double deficient mice, we identified selective contributions of RIP1 to an accumulation of murine splenic Marginal Zone (MZ) B cells and B1-b cells. We used mixed bone-marrow chimeras to determine that innate B cell commitment required B cell-intrinsic RIP1, RIP3, and caspase-8 sufficiency. RIP1 regulated MZ B cell development rather than differentiation and RIP1 mediates its innate immune effects independent of the RIP1 kinase domain. NP-KLH/alum and NP-Ficoll vaccination of mice doubly deficient in both caspase-8 and RIP3 or deficient in all three proteins (RIP3, caspase-8, and RIP1) revealed uniquely delayed T-dependent and T-independent IgG responses, abnormal splenic germinal center architecture, and reduced extrafollicular plasmablast formation compared to WT mice. Thus, RIP kinases and caspase-8 jointly orchestrate B cell fate and delayed effector function through a B cell-intrinsic mechanism.

Highlights

Pathogenic missense/nonsense mutations in the Receptor Interactor Protein kinase (RIP) 1 gene have recently been linked to a novel autoinflammatory disease in humans dubbed Cleavage resistant RIP1 Induced Autoinflammatory (CRIA) disease
Mice can be rescued by Ripk3 depletion to produce viable mice with a normal mendelian frequency of offspring capable of living well into adulthood [17, 20]
We found that RIP3-/, DKO and TKO mice displayed disrupted germinal center (GC) architecture compared to wild-type mice (Figure 5F)

Summary

Introduction

Pathogenic missense/nonsense mutations in the Receptor Interactor Protein kinase (RIP) 1 gene have recently been linked to a novel autoinflammatory disease in humans dubbed Cleavage resistant RIP1 Induced Autoinflammatory (CRIA) disease. Another study has linked biallelic mutations in human RIP1 to inflammatory bowel disease and combined immunodeficiency through altered inflammasome and NFkB activity [2, 3]. RIP1 can play contrasting roles directing cell death or mediating pro-survival signals depending on context. Together with caspase-8, RIP1 conveys signals for apoptotic cell death while RIP1 and RIP3 interactions mediate signaling for necroptosis. On the other hand, ubiquitinated RIP1 can mediate pro-survival signals through NFkB gene expression [5]. RIP3, a kinase in the same family, lacks the DD and is essential for necroptotic cell death. The scaffold domain of RIP1 can prevent kinase independent activation of caspase-8 and RIP3, adding another layer of signal regulation [6]

Methods

Results

Conclusion