Functional Dissection of the Dominant Role of CD55 in Protecting Vesicular Stomatitis Virus against Complement-Mediated Neutralization.

Nisha Asok Kumar,Joydeep Nag,John Bernet Johnson,Umerali Kunnakkadan,Reshma Koolaparambil Mukesh,Douglas S Lyles,Sreenath Muraleedharan Suma

doi:10.3390/v13030373

Abstract

The human complement system is an important part of the innate immune system. Its effector pathways largely mediate virus neutralization. Vesicular stomatitis virus (VSV) activates the classical pathway of the complement, leading to virus neutralization by lysis. Two host-derived membrane-associated regulators of complement activation (RCA), CD55 and CD46, which are incorporated into the VSV envelope during egress, confer protection by delaying/resisting complement-mediated neutralization. We showed previously that CD55 is more effective than CD46 in the inhibition of neutralization. In this study, we identified that, at the protein level, VSV infection resulted in the down-regulation of CD46 but not CD55. The mRNA of both the RCAs was significantly down-regulated by VSV, but it was delayed in the case of CD55. The immunoblot analysis of the levels of RCAs in the progeny virion harvested at three specific time intervals, points to an equal ratio of its distribution relative to viral proteins. Besides reconfirming the dominant role of CD55 over CD46 in shielding VSV from complement, our results also highlight the importance of the subtle modulation in the expression pattern of RCAs in a system naturally expressing them.

Highlights

Innate immune barriers, including the complement system, act as the front line defense against viral infections
In order to determine whether there are changes in the expression of CD46 and CD55 in infected cells with respect to time, HeLa cells were infected with Vesicular stomatitis virus (VSV) at an Multiplicity of Infection (MOI) of 10, and whole cell lysates were collected at every one hour interval up to 24 h
The complement system plays a pivotal role as a first line of defense against invading pathogens, including viruses, and contributes enormously in stimulating the adaptive immune responses

Summary

Introduction

Innate immune barriers, including the complement system, act as the front line defense against viral infections. The activation and amplification of complement pathways can result in the assembly of the lytic complex called the membrane attack complex (MAC) [1,2] on the surface of viruses and infected cells, leading to lysis [3]. Besides the MAC mediated lysis of pathogens or infected cells, the active mechanisms of pathogen clearance by complement include: (a) the opsonization of pathogens for phagocytosis, (b) the production of anaphylotoxins (e.g., C5a, C3a), (c) aggregation, and (d) the activation and regulation of T and B cell responses [3,4,5]. The upstream complement components of the classical pathway, including C1, C2, C4 and C3, were found to be essential for VSV neutralization [6,7,8]. It has been demonstrated that the involvement of complement components (C3, C4) and complement receptors (CR2, CR3 and CR4) in the resident macrophages in the marginal zones of the secondary lymphoid organs is pivotal in the engagement of B-cell specific responses during VSV infection [12]

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