A Fish Leukocyte Immune-Type Receptor Uses a Novel Intracytoplasmic Tail Networking Mechanism to Cross-Inhibit the Phagocytic Response.

Chenjie Fei,Myron A Zwozdesky,James L Stafford

doi:10.3390/ijms21145146

Chenjie Fei, Myron A Zwozdesky + Show 1 more

Open Access

https://doi.org/10.3390/ijms21145146

Copy DOI

Abstract

Channel catfish (Ictalurus punctatus) leukocyte immune-type receptors (IpLITRs) are a family of immunoregulatory proteins shown to regulate several innate immune cell effector responses, including phagocytosis. The precise mechanisms of IpLITR-mediated regulation of the phagocytic process are not entirely understood, but we have previously shown that different IpLITR-types use classical as well as novel pathways for controlling immune cell-mediated target engulfment. To date, all functional assessments of IpLITR-mediated regulatory actions have focused on the independent characterization of select IpLITR-types in transfected cells. As members of the immunoglobulin superfamily, many IpLITRs share similar extracellular Ig-like domains, thus it is possible that various IpLITR actions are influenced by cross-talk mechanisms between different IpLITR-types; analogous to the paired innate receptor paradigm in mammals. Here, we describe in detail the co-expression of different IpLITR-types in the human embryonic AD293 cell line and examination of their receptor cross-talk mechanisms during the regulation of the phagocytic response using imaging flow cytometry, confocal microscopy, and immunoprecipitation protocols. Overall, our data provides interesting new insights into the integrated control of phagocytosis via the antagonistic networking of independent IpLITR-types that requires the selective recruitment of inhibitory signaling molecules for the initiation and sustained cross-inhibition of phagocytosis.

Highlights

Performed by macrophages, phagocytosis is an evolutionarily conserved innate protective mechanism that results in the destruction of microbial intruders, and it is a cellular process that facilitates the removal of dead cells from the host following infection/inflammation-mediated tissue damage [1]
Excessive production of pro-inflammatory cytokines and highly reactive tissue-damaging products during phagocytosis is detrimental to host tissues, it is no surprise that this process is strictly regulated to mitigate unnecessary collateral host damage [9].One key regulatory mechanism controlling innate immune cell effector responses during inflammation is antagonistic receptor cross-talk
This is consistent with phenotypes observed in AD293 cells solely expressing phenotypes observed in AD293 cells solely expressing 2.6b ITAM cytoplasmic tail (CYT) and 1.1bWT CYT [24] and rules out the possibility of cross-reactivity between α-HA and α-FLAG mAbs in these assays

Summary

Introduction

Performed by macrophages, phagocytosis is an evolutionarily conserved innate protective mechanism that results in the destruction of microbial intruders, and it is a cellular process that facilitates the removal of dead cells from the host following infection/inflammation-mediated tissue damage [1]. Excessive production of pro-inflammatory cytokines and highly reactive tissue-damaging products (e.g., reactive oxygen species) during phagocytosis is detrimental to host tissues, it is no surprise that this process is strictly regulated to mitigate unnecessary collateral host damage [9].One key regulatory mechanism controlling innate immune cell effector responses during inflammation is antagonistic receptor cross-talk. Activating receptors (e.g., FcγRIIA) are often co-crosslinked with inhibitory counterparts (e.g., FcγRIIB) during the phagocytic process [10] This results in the recruitment of inhibitory signaling molecules (e.g., SHIP, SHP-1/2 phosphatases) to sites of cell-target contact (i.e., the phagocytic synapse) that serve to down-regulate phagocytosis and control the secretion of bioactive and antimicrobial molecules [10,11,12]. The mechanistic details responsible for regulating antimicrobial responses, such as phagocytosis, are not fully understood and studies using alternative vertebrate models may provide new insights into conserved and divergent aspects of receptor cross-talk mechanisms

Methods

Results

Conclusion