A comparison of lymphocyte subset distribution in rat lacrimal glands with cells from tissues of mucosal and non-mucosal origin

Ocular Mucosal Immunity

Mucosal immunity defends the ocular surface against antigenic challenge and microbial invasion. The principal effector site is the lacrimal gland, where immunoglobulin A (IgA) antibodies are produced. Nasal-associated lymphoid tissue and posterior cervical lymph nodes function as major inductive sites for tear IgA responses. Neural connections and systemic hormones maintain the integrity and function of the ocular surface. Neuroenzyme activities in the lacrimal gland are influenced by ocular infections, leading to reduced expression of acetylcholine and modulation of receptors on acinar cells and on plasma cells, thereby decreasing fluid and immunoglobulin secretion. T lymphocyte-dependent responses result in production of interleukin-4 in lacrimal glands, thereby influencing cholinergic enzyme activity affecting immune processes and lacrimal physiology. Furthermore, neuropeptides released into lymphoid structures or inflamed tissues are chemotactic for antigen-presenting cells and affect their interactions with T cells. Thus, in developing therapeutic approaches for treating dry-eye conditions and vaccination strategies to elicit protective ocular mucosal immune responses, the entire lacrimal functional unit should be considered.

Development of a high-throughput screening assay for inhibitors of aggrecan cleavage using luminescent oxygen channeling (AlphaScreen )

Aggrecan is one of the most important structural components of joint cartilage, and members of the metalloprotease (MMP) and ADAM (a disintegrin and metalloproteinase) protease families have been shown to degrade aggrecan in vivo. A robust assay for aggrecan-degrading activity suitable for high-throughput screening (HTS) was set up and measured using AlphaScreen. In this technology, beads brought into proximity through cross-linking and stimulated with laser light generate a signal through luminescent oxygen tunneling, the outcome of which is a time-resolved fluorescent signal. Specific antibodies to the carbohydrate side chains of aggrecan were harnessed to create a scaffold whereby aggrecan could form a cross-link between donor and acceptor AlphaScreen detector beads. Digested aggrecan, which failed to form a cross-link, generated no signal, so that inhibitors of the digestion could be detected as a restoration of signal. The development of this assay and its validation for HTS are described in this report.

Lymphocyte subsets in conjunctival mucosa-associated-lymphoid-tissue after exposure to retinal-S-antigen

PURPOSE

To evaluate the immune cell subsets in conjunctival mucosa-associated-lymphoid-tissue (C-MALT) following challenge with antigen.

METHODS

Ten adult female Lewis rats were studied. Five rats received one drop (5 microL) of retinal S-antigen (500 microg/mL in phosphate buffered saline, PBS) instilled into the lower fornix twice daily for 10 consecutive days. Five rats received PBS only and served as controls for the experiment. Two days after the last instillation the animals were sacrificed and the orbital contents prepared for immunohistological staining. A panel of monoclonal antibodies was used: CD5, CD4, CD8, CD25, and CD45RA. The number of positive cells were counted in sections of epibulbar, forniceal, and tarsal conjunctiva.

RESULTS

There was a significant increase in the number of CD8+ T lymphocytes in the conjunctiva of animals receiving retinal S-antigen when compared to control animals.

CONCLUSION

Conjunctival instillation of retinal S-antigen causes an immune response in the C-MALT with a significant increase in the CD8+ T lymphocyte subset in this tissue. This response may be involved in the induction of tolerance to the encountered antigen.

Mucosal defense of the outer eye

A combination of mechanical, anatomical, immunological, and microbiological factors prevent infection of the outer eye. Mechanical and anatomical factors include the intact epithelium of the conjunctiva and cornea and the constant blinking action of the eyelids. Tear components that play a role in eye defense include lysozyme, immunoglobulins, lactoferrin, and betalysin. The normal bacterial flora of the conjunctiva may also have an inhibitory effect on the survival of more pathogenic species. The eye is linked to the common mucosal immune system, thus gaining the benefits of a system of microbial defense which is primed in the gastrointestinal tract, where a continuing large antigen load is capable of stimulating ongoing immune protection. The relative roles of the various factors contributing to prevention of eye infection remain to be fully defined.

Phenotypic analysis of resident lymphoid cells in the conjunctiva and adnexal tissues of rat

The conjunctival associated lymphoid tissue is considered to be an integral part of the mucosal immune system. Under normal circumstances immune mechanisms in mucosal associated lymphoid tissue of the gut and bronchus can selectively suppress, rather than enhance, immune responsiveness to encountered antigens, inducing a state of tolerance. It is possible that conjunctival associated lymphoid tissue can also induce a state of tolerance to encountered antigens. Such a response may be exploited to modulate immune mediated ocular disease. Enhanced tolerance may protect the host against foreign antigen. Alternatively, under certain circumstances when the normal immune system is altered or disrupted the mucosal tissue may act to induce sensitisation and trigger immune mediated disease. The rat is frequently used as an animal model of immune mediated eye disease, but the normal profile of immune cells in the rat conjunctiva has not been studied. This information is essential for meaningful interpretation in the experimental situation. In this study we examined the immunophenotype of lymphoid tissue associated with the conjunctiva, lacrimal gland and Harderian gland of the Lewis rat. CD4+, Ia+ and the monocyte/macrophage population of cells were found predominantly in the substantia propria of the conjuctiva and interstitial connective tissue of the glands. CD8+ cells were distributed mainly in relation to the conjunctival and glandular epithelium. Goblet cells stained strongly with the monoclonal antibody (MAb) MRC OX-39, which is a marker for IL-2 receptors. The overall pattern of distribution of immunocompetent cells in the rat was found to be similar to that reported in humans.

Nasal-associated lymphoid tissue is an inductive site for rat tear IgA antibody responses

The role of nasal-associated lymphoid tissue (NALT) as a mucosal inductive site for tear IgA antibody responses was investigated in the rat model. Fluorescent microspheres were shown to access and be taken up by NALT after intranasal of ocular-topical administration, although fewer microspheres were found in the latter case. Tear IgA anti-DNP antibody responses to dinitrophenylated Streptococcus pneumoniae were 6 micrograms/ml at day 7, 10 micrograms/ml at day 10, and were still detectable on day 21 (5 micrograms/ml) following ocular or gastrointestinal immunization. Intranasal immunization induced tear IgA responses which were 1.7-fold higher at day 7 (10 micrograms/ml), peaked by day 10 (14 micrograms/ml) and were still 1.6-fold higher (8 micrograms/ml) at day 21 than responses of ocular or gastrointestinal groups. These findings suggest that intranasal immunization may be more effective than ocular or gastrointestinal administration in eliciting tear IgA antibody responses and, taken together with the microsphere data, indicate that NALT can serve as an inductive site for ocular mucosal IgA responses.

Phenotypic profiles of lymphocyte populations isolated from rat major salivary glands

Marker expression was studied in rat lymphocyte populations isolated from parotid, submandibular and sublingual salivary glands. Comparative data were also obtained for lacrimal gland and spleen populations. Increased percentages of Thy-1+ cells were found in salivary gland populations when compared to spleen with the highest percentage noted for parotid gland. Thy-1 percentages in parotid gland were comparable to those obtained with lacrimal gland. Salivary gland sIg, CD5 and CD8 cell percentages were lower than those obtained for lacrimal gland and splenic populations. The percentages of CD4-bearing cells in submandibular and sublingual gland were lower than those found in parotid gland, lacrimal gland and spleen, and the CD4:CD8 ratios in parotid gland most closely approximated those in spleen. Increased percentages of Thy-1+ lymphocytes coexpressing sIg and CD5 were obtained for all salivary gland cell populations when compared to spleen; however, percentages of salivary gland cells bearing these 3 markers were lower than noted for lacrimal gland, which contained the highest percentage. With respect to adhesion molecules, lymph node homing receptor (LNHR) and Peyer's patch homing receptor (PPHR) bearing cells were found in all glandular populations with the percentages of LNHR+ exceeding PPHR+ lymphocytes. Homing receptor bearing populations were highest in spleen and were present in equal proportions. LFA-1 was expressed by all salivary gland cell populations in greater percentages than lacrimal gland, but lower than those in spleen. VLA-4 and CD44 expression was higher in parotid gland and spleen than in submandibular and lacrimal gland. These data show that the phenotypes of resident lymphocytes in salivary gland tissues differ from lacrimal gland and spleen, as well as each other, and indicate that Thy-1+ cells in glandular tissues bear both B and T cell markers. The adhesion molecule expression data suggest that these molecules may be utilized differently in various glandular tissues, potentially contributing to the variation in phenotypic profiles of resident glandular lymphocytes.

The effects of transforming growth factor-beta and interleukins 2, 5 and 6 on immunoglobulin production in cultured rat salivary gland tissues

The effects of transforming growth factor-beta, alone, and in combination with selected interleukins on immunoglobulin production were investigated using an in vitro rat tissue fragment culture system with either parotid, submandibular or sublingual gland tissue. In the majority of culture groups, TGF-beta alone, or in combination with either interleukin 2 (IL-2), IL-5, IL-6 or IL-5 and IL-6 together, significantly increased immunoglobulin A (IgA) levels over those obtained in untreated cultures. The levels of IgG and IgM were generally not affected, with the exception of one sublingual and two submandibular groups(s), where cytokine administration up-regulated either IgG or IgM production. These data indicate that transforming growth factor-beta in combination with IL-2, IL-5, IL-6 or IL-5 and IL-6 can exert a stimulatory effect on IgA production in vitro, supporting a potential regulatory role for these cytokines in salivary gland IgA responses.