Ocular exposure to infectious laryngotracheitis virus alters leukocyte subsets in the head-associated lymphoid tissues and trachea of 6-week-old White Leghorn chickens

Abstract

ABSTRACT Infectious laryngotracheitis virus (ILTV), an alphaherpesvirus, causes acute respiratory disease primarily infecting the upper respiratory tract and conjunctiva. Administration of live attenuated ILTV vaccines via eye drop, drinking water, or by coarse spray elicits protective mucosal immunity in the head-associated lymphoid tissues (HALT), of which conjunctiva-associated lymphoid tissue (CALT) and the Harderian gland (HG) are important tissue components. The trachea, a non-lymphoid tissue, also receives significant influx of inflammatory cells that dictate the outcome of ILTV infection. The objective of this study was to evaluate leukocyte cellular and phenotypic changes in the CALT, HG and trachea following ocular infection with a virulent ILTV strain. At 1, 3, 5, 7 and 9 days post-infection, CALT, HG, and trachea of 6-week-old specific pathogen free (SPF) chickens ocularly-exposed to vehicle or virulent ILTV strain 63140 were dissociated, the cells enumerated and then phenotyped using flow cytometry. The CALT had the highest viral genomic load, which peaked on day 3. In ILTV-infected birds, the CALT had a decreased percentage of leukocytes. This was reflected by decreased numbers of MHCI+MHCII–, MHCI+MHCIIlow+, and CD4+ cells, while IgM+ and MHCI+MHCIIHigh+ expressing cell populations increased. In the HG, the most notable change in cells from ILTV-infected birds was a decrease in IgM expressing cells and histologically, an increase in Mott cells. In summary, an acute, ocular exposure to ILTV strain 63140 in young birds shifts subsets of lymphocyte populations in the CALT and HG with minimal impact on the trachea.