Louane E. Hann

Hormonal influence on the secretory immune system of the eye: Endocrine impact on the lacrimal gland accumulation and secretion of IgA and IgG

The objective of the current investigation was to explore the processes underlying the androgen control of tear IgA and to determine whether hormone exposure also modifies tear IgG content. In addition, studies evaluated the impact of diabetes on the androgen regulation of secretory immunity in the eye. Tears and lacrimal glands were collected from age-matched, adult male rats, which had undergone hypophysectomy, selective ablation of the anterior pituitary, streptozotocin-induced diabetes, sham-surgery and/or orchiectomy and had been exposed to vehicle or physiological amounts of testosterone for varying periods of time. Our findings demonstrated that testosterone administration selectively increased the accumulation of IgA, but not IgG, in tears and lacrimal glands of orchiectomized rats. This hormone effect was associated with a 2-fold enhancement of the IgA transfer from lacrimal tissue to tears; IgA movement was against a gradient. In contrast, androgen exposure had no significant influence on the lacrimal gland/tear transfer of IgG, which was down a 90-fold gradient. Testosterone action on the lacrimal gland appeared to involve an increase in IgA production, but not a consistent alteration in the total number of IgA-containing cells. Similarly, androgen exposure had no impact on the population of IgG-containing lymphocytes in lacrimal tissue. Of interest, ablation of the anterior or entire pituitary in orchiectomized rats, which procedure inhibits testosterone-induced stimulation of tear IgA levels, significantly reduced the total number of IgA-containing cells in the lacrimal gland. Induction of diabetes by streptozotocin injection to orchiectomized rats resulted in diminished tear IgA content and decreased numbers of lacrimal IgA-positive lymphocytes, but did not prevent the testosterone-associated rise in IgA antibody content. In summary, our findings demonstrate that androgens increase the lacrimal gland production and secretion of IgA, but not IgG.

Age- and gender-related influence on the lacrimal gland and tears.

Abstract Previous research has demonstrated that distinct, gender‐related differences exist in lacrimal glands in a variety of adult species. The objective of the current investigation was to examine whether this influence of gender extends throughout development and aging. Towards that end, morphological parameters of the lacrimal gland, as well as the volume, protein and IgG content of tears, were measured in male and female infant, pre‐weanling, pubertal, adult, mid‐life and senescent rats. Our results showed that dramatic, age‐related variations occured in the weight and morphological appearance of the lacrimal gland. Moreover, the magnitude of structural changes was dependent upon gender. Acinar area was significantly greater in lacrimal tissue of males, as compared to females, at all ages except pre‐weanling; this sexual dimorphism was most evident in senescent rats. In contrast, acinar density in lacrimal glands of females was higher than, or equal to, that of males throughout development and aging. With regard to tears, promounced increases were evident in tear volume, protein and IgG content from the pre‐weanling stage to adulthood. After this time, these tear indices tended either to plateau or rise slightly until senescence. Gender had little or no impact of the volume of, or protein and IgG level in, tears. Of interest, the IgG/protein ratio in tears was 49– to 105–fold less than that found in lacrimal tissue, indicating that IgG moves down a gradient from the lacrimal gland to tears. Overall, our findings demonstrate that gender has a significant influence on lacrimal gland structure during development and aging. However, this impact is limited with respect to tear volume and protein content.

Impact of aging and gender on the lg-containing cell profile of the lacrimal gland

Abstract. The present study investigated the influence of age and gender on the number of IgA‐ and IgM‐containing cells in the lacrimal gland. Tissues were obtained from male and female rats at 0.2 (infant), 0.6 (pre‐pubertal), 1.3 (pubertal), 3 (adult), 8 (mid‐life) and 17 (senescent) months of age, then processed for immunofluorescence microscopy. No IgA‐containing cells could be detected in lacrimal glands from infant rats, but a significant accumulation had occurred by 0.6 months of age. The extent of this increase was gender‐dependent: tissues from male rats had significantly higher IgA‐positive cell densities than those of females. After 0.6 months of age, no further variations in the density of IgA‐containing lymphocytes were observed in female gland. In contrast, male glands exhibited marked fluctuations in the density of IgA‐containing lymphocytes during the time period spanning puberty (0.6 → 3 months). Of interest, the frequency distibution of IgA‐containing cells in tissue sections was not uniform in rats older than 0.2 months. Correction of cell densities for age‐related elevations in lacrimal gland weight demonstrated that the total accumulation of IgA‐containing cells was both age‐ and gender‐related. Highest cell numbers were attained at 3 months in females and 3 and 17 months in males. Moreover, at all assessed ages, the total IgA‐containing cell number in glands of males was greater than, or equal to, that in tissues of females. In contrast to the IgA‐positive cell profile, no age‐ or gender‐associated differences were apparent in the number of IgM‐containing cells in the lacrimal gland. These findings demonstrate that both age and gender exert a significant impact on the population of IgA‐, but not IgM‐, containing cells in lacrimal tissue.

Characterization of functional melanotropin receptors in lacrimal glands of the rat

The specific melanotropin (MSH) binding sites of rat lacrimal glands were characterized with respect to anatomic distribution, peptide specificity and selectivity, and coupling to a biological response. Tissue distribution of MSH binding sites was determined by autoradiography following in situ binding of a radiolabeled, biologically active preparation of a superpotent alpha-MSH analog, [125I]-[Nle4,D-Phe7]-alpha-MSH ([125I]-NDP-MSH). Intense, specific (i.e., alpha-MSH-displaceable) [125I]-NDP-MSH binding was observed throughout lacrimal acinar tissue, but not in ducts or stroma. In freshly isolated lacrimal acinar cells, specific binding of [125I]-NDP-MSH was maximal within 30 min and rapidly reversible, with a dissociation half-time of about 15 min. A number of melanotropins [alpha-MSH, [N,O-diacetyl-Ser1]-alpha-MSH, [des-acetyl-Ser1]-alpha-MSH, beta-MSH, ACTH(1-24) and ACTH(1-39)] were recognized by these binding sites, as assessed by their inhibition of [125I]-NDP-MSH binding; NDP-MSH was the most potent (IC50 = 1.3 x 10(-9) M). In contrast, other peptides, including ACTH(4-10) and the nonmelanotropic peptides VIP, substance P, somatostatin, and ACTH(18-39) (CLIP), had no effects on tracer binding. In isolated lacrimal acinar cells, alpha-MSH and NDP-MSH stimulated intracellular cyclic AMP accumulation. We conclude that lacrimal acinar cells express functional receptors recognizing melanotropins, suggesting that the lacrimal gland may be a target for physiological regulation by endogenous melanotropins.

Production and Utilization of a Mouse Monoclonal Antibody to RAT IgA: Identification of Gender-Related Differences in the Secretory Immune System

The present study was designed: to produce a mouse monoclonal antibody to rat IgA; and to examine, by using the monoclonal antibody, possible gender-related differences in the secretory immune system. Hybridomas were prepared that secreted mouse monoclonal antibodies directed specifically against rat IgA. These antibodies were identified as IgG1 and kappa chain positive and could be used to purify rat IgA by affinity chromatography, detect tissue IgA by immunofluorescence and measure IgA levels in external secretions by radioimmunoassay. In utilizing these antibodies, we found that a distinct, gender-related difference exists in the number of IgA-containing cells in the rat lacrimal gland. Lacrimal tissue from male rats had a significantly higher content of IgA-positive cells than did that from female rats. This difference correlated well with our previous observations on the sexual dimorphism in tear IgA levels. We also observed in the present study that gender-associated variations in IgA content occur in respiratory secretions. In contrast to the eye, however, females had significantly greater IgA concentrations than did males. No effect of gender was found on IgA levels in small intestinal secretions, saliva or serum. Overall, our results indicate that gender may play a role in the immune response of specific mucosal tissues.

Endocrine Regulation of the Ocular Secretory Immune System

Past research has demonstrated that androgens stimulate the accumulation of both IgA and secretory component (SC) in tears of rats (1,2). This hormone action appears to be due to an enhancement of the synthesis and/or secretion of IgA and SC by the lacrimal gland (2,3) and seems to underly the sexual dimorphism known to exist in the ocular secretory immune system (1–4). However, whether this hormonal effect is unique to the eye or is shared by other mucosal sites has not been determined.

Androgen regulation of the ocular secretory immune system

The principal tissue involved in secretory immune system of the eye is the lacrimal gland [l].This tissue, which is the origin of tear IgA and secretory component (SC) [2,3], possesses a high density of IgA plasma cells, a smaller population of IgG- and IgM-containing cells and a diverse array of T lymphocytes [4,5]. In addition, acinar and ductal cells produce SC [6,7], which appears to regulate the binding and transport of polymeric IgA into tears against an apparent concentration gradient [8,9].