Selectivity, specificity and kinetics of the androgen regulation of the ocular secretory immune system

The purpose of the present investigation was to determine the selectivity, specificity and kinetics of the androgen regulation of the ocular secretory immune system. To examine the mucosal selectivity of hormone action, tears, saliva, respiratory and intestinal secretions, urine and serum were collected from orchiectomized rats following four days of treatment with saline or testosterone. Androgen administration significantly increased the tear levels of IgA and free SC. In contrast, this combined hormone response was not duplicated in other mucosal secretions or serum. Consequently, it appears that the androgen control of the ocular secretory immune system is unique to the eye. To evaluate androgenic specificity, orchiectomized rats were treated for four days with saline, testosterone, 5 alpha-androstan-17 beta-o1 ('5 alpha'), 4-estren-7 alpha-methyl-17 beta-o1-3-one ('4-E') or the synthetic analogue, danazol. Results demonstrated that testosterone and '4-E', a potent androgen, both stimulated the accumulation of tear IgA and free SC, compared to amounts in tears of saline-treated controls. The weak androgen '5 alpha' induced a slight rise in tear free SC, but not IgA, levels, whereas danazol had no effect on the ocular secretory immune system. These findings indicate that androgen structure is of critical importance in modulation of mucosal immunity in the eye. Lastly, to assess the kinetics of hormone action on tear IgA and free SC, orchiectomized rats were acutely (0, 1.5, 4, 7, 12, or 24 hours) or chronically (0, 4, 7, 11, 14, or 17 days) exposed to testosterone. Acute androgen exposure for less than 12 hours did not elicit any change in the tear content of IgA or free SC. In comparison, chronic androgen treatment induced a progressive and dramatic rise in the levels of both tear proteins. By 17 days of hormone exposure, the IgA and free SC concentrations in tears had increased by 14- and 18-fold amounts, respectively, relative to amounts in placebo-treated controls. Of interest, the temporal pattern of accumulation of tear IgA and free SC were different. Overall, these results show prolonged, but not abbreviated, exposure to androgens has a profound impact on the IgA and free SC profile in tears.     

Hormonal influence on the secretory immune system of the eye: endocrine interactions in the control of IgA and secretory component levels in tears of rats.

Previous research from our laboratory has demonstrated that androgens regulate the ocular secretory immune system of the rat. The purpose of the present study was to determine whether other hormones might influence this androgen effect. Experiments involved the daily administration of saline or hormones to adult orchiectomized rats, the collection of tears 24 hr after the fourth hormone injection, and the measurement of free secretory component (SC), IgA and total protein levels in tears. Our first aim was to evaluate whether female sex steroids might antagonize androgen action on tear IgA and SC: orchiectomized rats were treated with combinations of saline, testosterone, oestradiol or progesterone. Testosterone induced a significant increase in the tear SC and IgA concentrations, as compared to those of saline-injected controls. This androgen effect was not inhibited by co-treatment with oestradiol or progesterone, nor duplicated by the administration of these hormones alone. Our second aim was to assess whether the absence of certain hormones might alter tear SC and IgA levels, or influence the ocular response to androgen exposure: rats underwent orchiectomies and specific endocrine organ ablations or appropriate sham-surgery. Absence of the pituitary gland, but not the thyroid, adrenal or pineal glands, resulted in a significant decrease in tear SC, IgA and total protein content. In addition, removal of the thyroid or adrenal glands did not prevent the testosterone-associated increase in tear SC and IgA, although thyroidectomy or adrenalectomy did diminish the magnitude of the androgen response. In contrast, hypophysectomy completely blocked the effect of testosterone on both tear SC and IgA. These results indicate that the hypothalamic-pituitary axis may regulate, or mediate, the action of androgens on ocular immunity in the rat.     

IgA receptors in health and disease

The varied interaction of the Fc region of IgA with receptors confers this antibody class with many of its unique properties. The epithelial polymeric Ig receptor on mucosal epithelial cells transports polymeric immunoglobulin A (pIgA) produced by mucosal B cells to the mucosal surface where, in complex with the secretory component (SC), this secretory immunoglobulin A (SIgA) excludes the multitude of dietary, environmental, and microbial antigens that continuously bombard the mucosae. In health, this IgA-mediated exclusion not only forms the initial defence against infection, it also spares the systemic immune system from potentially deleterious responses to innocuous antigens which can otherwise culminate in inflammatory bowel disease or asthma. Beyond antigen exclusion, in closer encounters with antigens, IgA receptors play roles in protective immunity and disease. FcaRI is the principal myeloid IgA receptor and is responsible for differing IgA-mediated effector responses such as respiratory burst, degranulation, and phagocytosis variously by granulyoctes, monocytes, and macrophages. Furthermore an unknown IgA receptor specific for the secretory component (SC) elicits powerful effector responses from eosinophils. On dendritic cells, FcaRI participates in antigen presentation while on microfold cells, key cells in mucosal antigen presentation, another unknown IgA receptor functions in the transport of antigens across the mucosal epithelial barrier. The activity of another uncharacterized IgA1/IgD receptor on T cells may affect autoimmune disorders. The interplay of different IgA receptors affects immune complex deposition in the common renal disease immunoglobulin A nephropathy (IgAN). Finally, the therapeutic application of various IgA receptors has been sought in the areas of infectious disease, vaccines, and cancer.     

Augmentation of antibody-dependent cell-mediated cytotoxicity by anti-immunoglobulin. I. Relationship to target cell capping

The functional integrity of the local immune system in vitamin A-deficient (A-) rats was investigated. Secretory IgA levels in the intestinal fluid of A- rats were significantly lower than in controls. This and the decrease in intensity of immunofluorescent staining for secretory component (SC) in the intestinal cells was related to the duration of vitamin A deprivation. IgG levels in the intestinal fluid, and serum IgA and IgG levels were unaffected in deficiency. Moreover, when the response of animals to DNP50-BGG was evaluated, the local anti-DNP response in the intestine was markedly depressed. These defects may result from impaired synthesis of SC by epithelial cells. On the other hand, the serum antibody response in deficient animals was not noticeably different from that of the controls; if any, htere was a slight reduction in the affinity of antibody.     

Expression of IgA and secretory component in the normal and in adenocarcinomas of Fallopian tube, endometrium and endocervix

The occurrence and localization of IgA and secretory components (SC) were examined in the normal and in adenocarcinomas of Fallopian tube, endometrium and endocervix. IgA-containing immunocytes were identified in the stroma of 90% of normal Fallopian tubes. It is suggested that the Fallopian tube may have an immunological function and may, together with the endocervix, constitute the local secretory immune system of the female genital tract. IgA and SC were frequently demonstrated in the cytoplasm and luminal secretion of adenocarcinomas of the endocervix, endometrium and Fallopian tube. This study has shown a decrease in immunoreactivity of SC among poorly differentiated adenocarcinomas but has failed to demonstrate any correlation between the expression of IgA and the degree of differentiation of the tumours. Secretory component appears, therefore, to be more useful than IgA as an indicator of secretory activity and differentiation of adenocarcinomas of the female genital tract.     

Bifidobacterium adolescentis modulates the specific immune response to another human gut bacterium, Bacteroides thetaiotaomicron, in gnotobiotic rats

In order to investigate the capability of an autochthonous bacterium to modulate the host's immune response against the indigenous microfiora, the immunogenicity of two selected bacterial species of the human gut was investigated in a gnotobiotic rat model. Germ-free (GF) rats were monoassociated with either Bifidobacterium (B.) adolescentis or Bacteroides (B.) thetaiotaomicron and the development of bacteria-specific IgG and IgA in serum and specific secretory IgA (sIgA) in feces of the animals were measured. Knowing the antibody levels in gnotobiotic rats induced by monoassociation, we subsequently diassociated two groups of rats in order to investigate the impact of B. adolescentis on the immune reaction against B. thetaiotaomicron. One group was diassociated simultaneously with B. adolescentis and B. thetaiotaomicron, the second group was diassociated with these bacteria in sequence. In contrast to B. thetaiotaomicron, B. adolescentis was not able to induce a systemic immune response in monoassociated animals as evident from serum IgG and IgA. However, both bacterial species challenged the mucosal immune system as indicated by an increase in sIgA in the feces. The specific immune response to B. thetaiotaomicron was significantly lower in diassociated animals than in animals monoassociated with B. thetaiotaomicron. This effect was more pronounced in the rats, that had been associated sequentially. The presence of B. adolescentis down-regulated the humoral immunity to B. thetaiotaomicron.     

Human eosinophils express a receptor for secretory component. Role in secretory IgA-dependent activation

The existence of a functional receptor for secretory component (SC) on the eosinophil membrane might explain the preferential degranulation induced by secretory IgA (sIgA) when compared to serum IgA. Indeed, flow cytometry analysis revealed that purified human SC could bind to a subpopulation (4–59%) of blood eosinophils purified from 19 patients with eosinophilia. Binding of radiolabeled human SC could be competitively inhibited using unlabeled SC or secretory IgA but not with serum IgA or IgG. Immunoprecipitation and immunosorbent chromatography using human SC revealed the presence of a major component at 15 kDa in eosinophil extracts as well as in culture supernatants but not in neutrophils. The 15-kDa protein eluted from the human SC immunosorbent was able to bind to SC or to sIgA but not to serum IgA. Eosinophils preincubated with human SC or sIgA released eosinophil cationic protein (ECP) and eosinophil peroxidase (EPO) after addition of anti-SC or anti-IgA monoclonal antibody as respective cross-linking reagents. These results indicated that binding of free or complexed SC to human eosinophils could induce eosinophil degranulation. Furthermore, the dose-dependent inhibition by SC of mediator release induced by sIgA but not by serum IgA, suggested that the receptor for SC could be involved in the preferential degranulation mediated by sIgA. These results indicate a novel pathway of eosinophil activation and its potential involvement in mucosal immunity, particularly in inflammatory diseases associated with infiltration of eosinophils and the enhanced production of sIgA.     

Secretory immune responses in ageing rats. II. Phenotype distribution of lymphocytes in secretory and lymphoid tissues.

The distribution of lymphocyte phenotypes was examined in various tissues from weanling (21-35 days), adult (3-4 months), mid-life (10-12 months) and senescent (18-20 months) rats. Lymphoid tissues included peripheral blood, spleen, cervical, mesenteric and inguinal lymph nodes. Tissues associated with secretory immune responses were also examined, including submandibular and parotid salivary glands, extraorbital lacrimal glands and Peyer's patches. IgA, IgG and IgM B cells were determined by surface Ig staining. Total T cells (W3/13), T helper/inducer (Th) (W3/25), T suppressor/cytotoxic (Ts) (OX8) and immature T cells (Thy 1.1; OX7) were also evaluated. IgG B cells were significantly decreased in lymphoid tissues from the senescent rats, while the weanling group exhibited decreased levels of all three B-cell isotypes compared to adult animals. IgA B cells were significantly decreased in the secretory tissues of the senescent rats, while IgM B cells were increased in both the weanling and senescent groups. Total T-cell percentages were unaffected by ageing in any of the tissues. The only consistent alteration in the lymphoid tissues was a decrease in Thy 1.1-positive cells in the older groups compared to the weanling group. A decreased Th cell percentage was demonstrated in the salivary and lacrimal glands of the weanling and senescent groups. Decreases in Th/Ts ratios, as well as decreased numbers of plasma cell precursors in the secretory tissues of the aged rats, suggests that alterations in normal secretory immune responses may be expected to accompany the ageing process.     

Novel functions of the polymeric Ig receptor: well beyond transport of immunoglobulins

The polymeric Ig receptor (pIgR) ensures efficient secretion of polymeric IgA (pIgA) at mucosal surfaces. On basal to apical transport across epithelial cells, the pIgR extracellular domain is cleaved, releasing secretory component (SC) in association with pIgA. This finds its raison d'être in the recent observation that SC is directly involved in the protective function of secretory IgA. In addition, free SC exhibits scavenger properties with respect to enteric pathogens. However, although pIgR dedicates its life to mucosal protection, it also seems to permit pathogen entrance through the epithelial barrier. The multiple mechanisms that they are involved in make pIgR and SC instrumental to mucosal immunity.     

Production and characterization of recombinant IgA.

Existence of secretory immunity at the mucosal surfaces was first postulated in 1919. Since then experimental and clinical studies have indicated that it is immunoglobulin A (IgA) that provides the first line of immune defense at the mucosal surfaces. While a number of expression systems--including viral, plant and mammalian cells--have been used to produce recombinant IgA, we used the mammalian expression system to produce IgA1 and the three allotypes of IgA2. By introducing the gene coding for human secretory component (SC) into transfectants producing IgA1, we have generated a single mammalian cell system that produces covalently assembled secretory IgA (sIgA). Using pulse-chase analysis, we determined the covalent assembly pathways of IgA1, IgA2 and sIgA and identified some of the structural differences leading to the different assembly patterns. Using affinity purified proteins, we have shown that neither IgA1 nor any of the allotypes of IgA2 activate either the classical or the alternative complement pathways, but modulate the complement activity of IgG or IgM. The two N-linked glycosylation sites in IgA1 are not required for its binding to the polymeric Ig receptor (pIgR). Finally, we have shown that sIgA1 was more stable than dIgA1 in the gastrointestinal tract of mice, suggesting that SC provides resistance to IgA in the gastrointestinal tract.     

Resistance to bacterial and parasitic infections in the nutritionally compromised host

Over the past few years the relationships and interactions of diet, disease, and immunology are becoming better defined with the development and understanding of host defenses. Nutritional state, immunity, and disease all influence each other in the hospitalized patient, the elderly, and the young. Disease can alter nutritional needs and immune responses to antigens. The roles of both dietary excesses and deficiencies on cellular, secretory, and humoral immune responses are related to diseases and disease incidence in humans and experimental animals. Malnutrition alters incidence and severity of fungal, bacterial, viral, and parasitic pathogens. The mechanisms of altered disease resistance in nutritionally stressed animal models occurs via changes in the lymphoreticular endothelial system. The effects of common nutritional deficiencies, low protein, and low carbohydrate diets on antibody production, macrophage function, secretory IgA synthesis, and T-cell functions. Nutritional supplementation can increase lymphocyte function and decrease growth of some pathogens and tumors. Alternatively, obesity and high fat have roles in infectious disease and immunity.     

Significance of different J chain profiles in human tissues: generation of IgA and IgM with binding site for secretory component is related to the J chain expressing capacity of the total local immunocyte population, including IgG and IgD producing cells, and depends on the clinical state of the tissue

Most IgA producing cells in normal intestinal and nasal mucosa synthesize dimers or larger polymers as evidenced by 90% cytoplasmic affinity for secretory component (SC) in vitro and almost 100% J chain positivity. The comparable median figures for normal exocrine glands (salivary, lacrimal, lactating mammary) were 84% and 92%, respectively. Conversely, IgA immunocytes in the subepithelial areas of palatine tonsils and in other extraglandular tissues, such as inflamed gingiva and intestinal submucosa, showed only 16-28% SC binding capacity and 18-51% J chain positivity. Similarly decreasing J chain expression, from glandular to extraglandular sites, was revealed not only for IgM immunocytes but also for those producing IgD or IgG, particularly the latter. This observation indicated more extensive overall clonal maturation in tissues without glandular elements since J chain expression seems to be a feature of relatively early memory B cells. The results were supported by studies in patients with selective IgA deficiency. Inflammatory disease caused significantly reduced SC binding capacity of IgA cells, both in intestinal mucosa and tonsils; this change was paralleled by decreased J chain expression, not only for mucosal and tonsillar IgA cells but also for mucosal IgG cells, suggesting local appearance of more mature clones. The resulting change to production of monomeric IgA may adversely affect secretory immunity and thus contribute to perpetuation of chronic inflammatory disease.     

SIgA基础与临床研究进展

分泌型免疫球蛋白A(SIgA)是人类黏膜免疫的主要抗体,由双体IgA[IgA(d)]、J链和分泌片(SC)共价结合构成。J链和IgA(d)由局部活化B细胞产生,SC由黏膜上皮细胞合成;SC与J链共价结合后与IgA(d)形成二聚体结构即SIgA。SIgA与多种疾病的发生、发展密切相关。最新研究表明,SIgA与慢性鼻窦炎。反复呼吸道感染、消化道感染、泌尿生殖系统感染、肝胆疾病、癌症局部免疫、口腔尖周病、缺铁性贫血、偏头痛和银屑病等疾病都有密切的关系;环境和大气污染可导致人体SIgA水平低下,局部免疫力下降。调节SIgA水平有益于改善临床疾病黏膜免疫状况。     

Secretory immune responses in ageing rats. I. Immunoglobulin levels.

Immunoglobulin levels in saliva, serum and gastrointestinal perfusates were measured in groups of ageing CDF (F-344)Cr1BR rats. Four age groups were studied, including: (i) weanling (21-35 days), (ii) adult (3-4 months), (iii) midlife (10-12 months), and (iv) senescent (18-20 months). There was no difference in the mean salivary volume and protein levels in the three older groups of rats. Salivary IgA in the weanling rats was significantly lower, having not yet attained adult levels, while salivary IgG was decreased in the senescent group. No IgM was detected in saliva from any of the animals. Serum IgM was elevated in the midlife and senescent rats. In contrast, serum IgG was significantly decreased in the senescent group when compared to the adult or midlife animals. Significant elevations were noted in serum and intestinal perfusate IgA in the senescent rats when compared to the adult group. While salivary IgA from all groups was shown to be greater than 95% polymeric, only the weanling and senescent groups exhibited a tendency toward predominantly polymeric serum IgA (67-70%). The results define altered immunoglobulin profiles in aged rats in both secretory and systemic fluids, which could affect the immunocompetence of these animals.     

Nutritional deficiency, immunologic function, and disease.

Several experiments conducted by our group over a period of 6 years have shown that nutritional stress, especially protein and/or calorie deprivation, leads to many, often dramatic, changes in the immune responses of mice, rats, and guinea pigs. Chronic protein deprivation (CPD) has been shown to create an enhancing effect on the cell-mediated immune responses of these animals. Humoral responses under CPD conditions were most often found to be depressed, but sometimes were unaffected, depending on the nature of the antigen employed. Chronic protein deprivation, consistent with the pattern just mentioned, improved tumor immunity by depressing production of B-cell blocking factors, and, in at least one instance, resistance to development of mammary adenocarcinoma in C3H mice was associated with evidence of increased numbers of T suppressor cells. Profound nutritional deficits (less than 5% protein per total daily food intake) depressed both cellular and humoral immunity. Early, though temporary, protein deprivation caused a long-term depression of both cellular and humoral immunity also, with the humoral component being the first to recover. Manipulation of protein and calories was found to have a profound effect on certain autoimmune conditions. Diets high in fat and low in protein favored reproduction but shortened the life of NZB mice, whereas diets high in protein and low in fat inhibited development of autoimmunity and prolonged life. Chronic moderate protein restriction permitted NZB mice to maintain their normally waning immunologic functions much longer than mice fed a normal protein intake. Further, the low-protein diet was associated with a delay in development of manifestations of autoimmunity. Decreasing dietary calories by a reduction of fats, carbohydrates, and proteins more than doubled the average life span of (NZB X NZW)F1 mice, a strain prone to early death from autoimmune disease. Histopathologic studies using immunofluorescent microscopy revealed that the development of the renal lesions caused by the deposition of antigen-antibody complexes, which is so characteristic of these mice, was markedly delayed.     

Aging effects on secretory IgA immune responses

Studies of cellular and humoral components of the secretory immune system indicated dramatic decreases in the SIgA response to T-dependent antigens (i.e. DNP-BGG) in aged rats. Senescent rats (18-20 months old) showed comparable levels of SIgA anti-DNP antibody to adult animals after oral immunization with a T-independent antigen, DNP-FICOLL. The salivary SIgA responses to both antigens were substantially decreased in weanling rats (21-35 days) versus the adult rats. Significant anamnestic SIgA responses were shown after oral immunization with DNP-BGG in adult rats, but was not observed in the senescent and midlife (10-12 months) rats. In contrast, the DNP-FICOLL appeared incapable of eliciting a secondary SIgA response in any of the groups. Examination of immunoglobulin-containing cells (ICC) in secretory and lymphoid tissues indicated a generally decreased proportion of IgAICC and IgGICC in the secretory tissues from the senescent rats. IgAICC and IgGICC were within normal limits in the lymphoid tissues of the senescent rats. The results demonstrate a defect in the ability of aged rats to manifest an IgA response to T-dependent antigens administered at mucosal surfaces.     

Aging Effects on Secretory IgA Immune responses

Studies of cellular and humoral components of the secretory immune system indicated dramatic decreases in the SIgA response to T-dependent antigens (i.e. DNP-BGG) in aged rats. Senescent rats (18–20 months old) showed comparable levels of SIgA anti-DNP antibody to adult animals after oral immunization with a T-independent antigen, DNP-FICOLL. The salivary SIgA responses to both antigens were substantially decreased in weanling rats (21–35 days) versus the adult rats. Significant anamnestic SIgA responses were shown after oral immunization with DNP-BGG in adult rats, but was not observed in the senescent and midlife (10–12 months) rats. In contrast, the DNP-FICOLL appeared incapable of eliciting a secondary SIgA response in any of the groups. Examination of immunoglobulin-containing cells (ICC) in secretory and lymphoid tissues indicated a generally decreased proportion of IgAICC and IgGICC in the secretory tissues from the senescent rats. IgAICC and IgGICC were within normal limits in the lymphoid tissues of the senescent rats. The results demonstrate a defect in the ability of aged rats to manifest an IgA response to T-dependent antigens administered at mucosal surfaces.     

Immunity, vaccination and the avian intestinal tract

Defence of the intestinal mucosal surface from enteric pathogens is initially mediated by secretory IgA (SIgA). As oral immunization of non-replicating antigen induces minimal SIgA antibody titers, novel immunization strategies which selectively induce mucosal immune responses in mammals are now being assessed in chickens. The strategies reviewed include the route of antigen delivery, the incorporation of antigenic components in delivery vehicles, the inclusion of immunomodulators in the vaccine formula or in the diet, and manipulation of intestinal microflora. The differences in anatomical organization and immunological mechanisms between birds and mammals must be considered when manipulating avian intestinal immunity with the latest immunotechnologies developed for mammals. Our knowledge of the function and functioning of the avian mucosal system is discussed. Progress in our understanding of this system, the location of precursor IgA B cells and antigen sampling by these sites is not as advanced as knowledge of the mammalian system, highlighting the need for ongoing research into the avian application of novel vaccination strategies.     

Mucosal Immune System in Health and Disease

The mucosal immune system is characterized predominantly by the secretory antibody response and gut-associated lymphoid tissue, cellular part of the mucosal immune system. The secretory antibody system depends on local production and selective epithelial transport of secretory IgA and IgM. Furthermore, secretory antibodies and interactions between the intestinal epithelium and T cells are involved in the mucosal down-regulation of the systemic immune system. Neuropeptides play a crucial role in the regulation of mucosal immune responses. It is possible that impairment of the mucosal immune response contribu tes to the pathogenesis of various intestinal diseases, such as inflammatory bowel disease. Until recently, however, mucosal immunity received relatively little attention from both basic and clinical scientists. Further research on mucosal immunity seems to have promise in helping to provide new understanding of the immune mechanisms and pathogenesis of several gastrointestinal and systemic diseases.     

Mucosal defense mechanism in health and disease. Role of the mucosal immune system.

The mucosal immune system is characterized predominantly by the secretory antibody response and gut-associated lymphoid tissue, cellular part of the mucosal immune system. The secretory antibody system depends on local production and selective epithelial transport of secretory IgA and IgM. Furthermore, secretory antibodies and interactions between the intestinal epithelium and T cells are involved in the mucosal down-regulation of the systemic immune system. Neuropeptides play a crucial role in the regulation of mucosal immune responses. It is possible that impairment of the mucosal immune response contributes to the pathogenesis of various intestinal diseases, such as inflammatory bowel disease. Until recently, however, mucosal immunity received relatively little attention from both basic and clinical scientists. Further research on mucosal immunity seems to have promise in helping to provide new understanding of the immune mechanisms and pathogenesis of several gastrointestinal and systemic diseases.