Mucosal humoral and cellular immune defense mechanisms of the horse's upper respiratory tract against equine herpesvirus-1 infection

Equine herpesvirus-1 (EHV-1) remains a widespread and economically important cause of abortion in horses worldwide, despite the frequent use of commercial vaccines. Inhalation of infectious EHV-1 particles by a susceptible animal leads to replication of the virus within the permissive upper respiratory tract epithelium and this may give rise to either subclinical infection or overt clinical disease of the upper airways. This primary round of virus amplification precedes systemic spread of the pathogen by a leukocyte associated viremia which in turn, is a pre-requisite for the more devastating sequelae to EHV-1 respiratory tract infection: abortion, paresis or neonatal foal mortality. Little is known about the role of the mucosal immune system in the defense of the equine upper respiratory tract against colonization by EHV-1. This represents a fundamental gap in our understanding of the virus-host relationship, hindering attempts to protect horses more efficiently against EHV-1-related disease by vaccination. Characterization of the virus-specific humoral and cellular immune defenses of the horse following experimental inoculation with virulent EHV-1 (Army 183; A183) was the focus of this research study. The mucosal immunogenicity of two commercially available vaccine antigens was also evaluated.; EHV-specific secretory IgA, measured in respiratory secretions using an indirect quantitative ELISA was elicited at high levels and persisted for long periods following intranasal instillation of A183 into experimental horses. Multiple IgG subisotypes were also identified in nasal mucus, but generally at lower levels and with shorter half-lives. Importantly, virus neutralizing antibody activity was also demonstrable in convalescent respiratory secretions.; EHV-specific cytotoxic T lymphocytes (CTLs) were demonstrated following intranasal inoculation of young horses with A183 in several upper respiratory tract associated mucosal lymphoid tissues and draining lymph nodes. The greatest virus specific cytotoxic activity was associated with the nasopharyngeal tonsil and its surrounding lymphoid tissues. Understanding the role of the equine mucosal immune system in protecting the upper respiratory tract of the horse from EHV-1 infection is an essential step in developing immunization strategies for the protection of equids from herpesvirus upper respiratory tract infection and subsequent abortion.