Abstract
Purpose::
The immunoarchitecture of the lacrimal gland (LG) changes dramatically during pregnancy, i.e., lymphocytes proliferate away from their normal periductal sites in non-pregnant rabbits into the interacinar interstitium, where they collect in clusters. In addition, pregnancy is associated with a decrease in lacrimal fluid production, reduced concentration of PRL within the fluid, increased PRL immunopositivity within epithelial cells of interlobular ducts, and re-distribution of PRL from the apical- to the basal cytoplasm, adjacent to remaining periductal lymphocytes. These changes suggest that the hormonal changes of pregnancy orchestrate a change in LG immunophysiology analogous to that which the mammary gland undergoes as it prepares to increase IgA secretion during lactation. The present study was designed to test the hypotheses that the pregnancy-associated changes are maintained during lactation and that they are reversed following the cessation of lactation.
Methods::
New Zealand White rabbits were studied during pregnancy, lactation, and at 4- and 6-weeks after weaning. Controls were non-pregnant rabbits. Specimens were evaluated by light and electron microscopy, immunohistochemistry, Western blot analysis of lacrimal fluid and ocular surface examination.
Results::
LGs of lactating rabbits mimicked the features seen previously in term pregnant rabbits, as noted above. In rabbits at 4- and 6-weeks after weaning, PRL was no longer immunolocalized within ductal epithelial cells, but was strongly positive within the lumens of ducts. Western blots confirmed an increased concentration of PRL within lacrimal fluid by 6-weeks after weaning and strong immunopositivity for PRL within lacrimal acinar cells. Schirmer, Rose Bengal and TBUT scores were abnormal during pregnancy. Schirmer and Rose Bengal tests were essentially normal by 6 weeks after weaning; only TBUT remained somewhat abnormal.
Conclusions::
PRL appears to play diverse roles within the LG. During pregnancy and lactation PRL appears likely to function primarily in immunoactivation of periductal lymphocytes rather than being released to the ocular surface. As animals recover from pregnancy and lactation, LG acinar cells appear to heighten the release of PRL to the ocular surface, where it is known to function as a trophic factor for corneal health.
Keywords: lacrimal gland • immunomodulation/immunoregulation • cornea: tears/tear film/dry eye