Role of the Cell in Neutralization

Abstract

Viruses have evolved attachment sites which bind specifically to a particular component of the exterior surface of the cell, the cell receptor unit and allow them to get close enough to the cell to gain entry. Viruses are known to attach to the lipid (phosphotidylserine, phosphotidylinositol or GM ganglioside: VSV) or carbohydrate (sialyoligosaccharides attached to unknown proteins or glycolipids: influenza type A, B and C viruses, paramyxoviruses, polyomavirus, encephalomyocarditis virus, reoviruses), but most common is attachment to a protein moiety (see Lentz 1990). Information has been slow in coming but transfection of cloned genes for putative attachment proteins into cells to which viruses do not normally attach is providing unambiguous data. Attachment proteins are often those concerned with intercellular communication, particularly between cells of the immune system: intercellular adhesion molecule 1 (ICAM-1) is the attachment protein for rhinovirus, a member of the immunoglobulin superfamily for poliovirus, class I major histocompatibility complex (MHC) for Semliki forest virus, adenovirus and human cytomegalovirus (HCMV), class II MHC for lactic dehydrogenaseelevating virus (LDV), complement receptor (CR)2 the receptor for C3d, a degradation product of complement component 3 for Epstein-Barr virus, IgA receptor for hepatitis B virus, integrins for FM DV, CD4 for HIV-1, HIV-2, SIV, and membrane-bound IgM for murine leukaemia virus. Other cell receptor units are molecules concerned with homeostasis such as the β-adrenergic receptor for reovirus or the acetylcholine receptor for rabies virus (Lentz 1990). Some caution is needed in this area as the identification of cell receptors for viruses has in some cases yet to be confirmed; in addition a virus mav use more than one receptor, as described below.