Systematic Variations in Immune Response-Related Gene Transcript Abundance Suggest New Questions about Environmental Influences on Lacrimal Gland Immunoregulation

Abstract

Retrospective analyses were undertaken to assess the hypothesis that environmental variables influenced immunophysiological status of lacrimal glands from untreated female rabbits that had been housed out-of-doors until they were acquired for use as controls for experimental studies. Rabbits were euthanized within 5 days of arrival at University Vivaria. Glands were divided for histology and RNA extraction. Transcript abundances were determined with real time RT-PCR. Sections were stained for CD18 and rabbit thymic lymphocyte antigen. Environmental variables assessed were mean daily high temperature, low humidity, high temperature/low humidity ratio, and days with above average temperature/humidity ratio ("adverse days") during the prior 30 days. Spearman's analyses revealed numerous significant correlations. Numbers of T cells and abundances of mRNAs for CD8; CCL2, and CCL4; IL-1α and IL-1β; the T(H)1 cytokine, IL-2; and the T(H)2- and B cell cytokines, IL-4, IL-6, IL-10, APRIL, and BAFF, all increased with adverse days, while IFN-γ mRNA abundance decreased. Glands from the group exposed to the most adverse days remained free of immunopathological lesions. Glands from the group exposed to the highest temperatures fell above the regression curves for IL-4, APRIL, and BAFF calculated for the other groups and had significantly higher abundances of mRNAs for prolactin, IL-18, CCL21, CCL28, CXCL8, and CXCL13. One of six glands from this group contained small immune cell aggregates; the others appeared normal. The only gland that presented with frank histopathology was from a group that had experienced benign conditions. Increasing adverse days correlated with increasing abundances of transcripts, including mRNAs for IL-2, IL-10, and CD8, outside the T(H)1/T(H)2 paradigm. The findings raise intriguing questions as to whether and how such changes might be associated with homeostatic phenomena.