Edris Sabbadini

The Submandibular Gland: A Key Organ in the Neuro-Immuno-Regulatory Network?

The evidence for the integration of the submandibular gland (SMG) into the neuroimmunoregulatory network has been reviewed. In laboratory rodents, factors extracted from the SMG were shown to stimulate lymphocyte proliferation, to affect the weight of the thymus, spleen and lymph nodes and to induce immunosuppression in several in vivo animal models. The SMG produces significant quantities of nerve growth factor (NGF), epidermal growth factor (EGF), transforming growth factor-beta and kallikreins, which are secreted into the saliva and affect immune and mucosal tissues and nerve endings in the gastrointestinal tract. These factors play a role in regulating mucosal immuno/inflammatory response and in regeneration and healing. The major salivary glands also produce antimicrobial proteins and secretory IgA antibodies which are essential factors in mucosal host defense. SMG-derived NGF, EGF and glandular kallikrein are delivered into the bloodstream where they may act as important systemic immunoregulators and also have major regulatory influences on the central neuroendocrine system. There is evidence to indicate that EGF is involved in the regulation of gonadal function. Growth hormone, prolactin, androgens, thyroid hormone and corticosteroids regulate protein synthesis in the SMG, whereas secretory activity is regulated by sympathetic (alpha- and beta-adrenergic) parasympathetic (muscarinic) and peptidergic (substance P and vasoactive intestinal peptide) nerve fibers. Fluid and electrolyte secretion is promoted by parasympathetic, whereas protein secretion is stimulated by sympathetic nerve impulses. Steroid hormones and cytokines (interleukin-1 alpha, -beta, tumor necrosis factor, interferon-gamma) have a major regulatory influence on protein secretion, including the secretion of immunoglobulin into the saliva. The SMG interacts with the mucosal and systemic compartments of the immune system, with the central and peripheral nervous systems, with the pituitary gland, and with peripheral endocrine organs. These interactions enable the SMG to exert regulatory influences on immune/inflammatory reactions in the gastrointestinal tract, in the lungs, and possibly elsewhere. It is suggested that these functions make this gland a key regulatory organ in the neuroimmunoregulatory network. Evidence is increasing that the major salivary glands fulfill similar functions in other species, including humans.

Neuroimmunoregulation and natural immunity

The development and function of the immune system is regulated by neuroendocrine factors. Immune function may be divided into adaptive and natural immunity. Adaptive immune responses are driven by specific determinants of the antigen (epitopes), require 5-10 d to fully develop, and show an accelerated or memory response after repeated exposure to the same antigen. Natural immunity may be divided into host defense mediated by non-immune factors (e.g., antimicrobial proteins, enzymes, mucus etc.) and polyspecific responses of the immune system. This polyspecific response relies on natural antibodies and on some other serum proteins (e.g., lipopolysaccharide-binding protein-LBP, C-reactive protein-CRP), and on surface receptors of macrophages, natural killer cells and B and T lymphocytes for activation. Highly conserved homologous (crossreactive) epitopes, or homotopes for short, are recognized by the natural immune system. Natural antibodies, LBP, and CRP are capable of activating the entire immune system after combination with the appropriate homotope. During febrile illness natural immune host defense is promptly elevated because of the rapid rise of natural antibodies, LBP, and CRP in the serum. This is known as the acute phase response (APR), which is initiated by a sudden rise of cytokines in the circulation, such as IL-1, IL-6, and TNF-alpha. The cytokines act on the brain, the neuroendocrine system, and on other tissues and organs, which leads to fever and profound hormonal and metabolic changes. The hypothalamus-pituitary adrenal axis is activated and serves as the primary regulator of immune and inflammatory reactions. Insulin, glucagon, and catecholeamine levels are also raised. Bone marrow activity and leukocyte function are high and the liver is converted to the rapid production of acute-phase proteins (APP). APP include LBP, CRP, fibrinogen, some complement components, enzyme inhibitors, and anti-inflammatory proteins, which may rise in the serum from several hundred to a thousand times within 24-48 hr. Therefore, natural immunity is a polyspecific response to homotopes, which functions as an instantaneous defense mechanism in health and which is rapidly boosted by cytokines and hormones during febrile illness. This is a highly successful defense reaction, as in the overwhelming majority of cases, febrile illness leads to recovery and the development of adaptive immunity in man and higher animals.

Purified human early pregnancy factor from preimplantation embryo possesses immunosuppressive properties

This study was undertaken to determine whether early pregnancy factor secreted by preimplantation embryos has immunosuppressive properties. Human early pregnancy factor was purified from embryo growth media of in vitro fertilized ova with ion-exchange and gel filtration chromatography. During each step of purification the fractions were tested for (1) early pregnancy factor activity with the rosette inhibition assay, (2) immunosuppressive properties with a concanavalin A-stimulated lymphocyte proliferation assay, and (3) purity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Results indicate that (1) human early pregnancy factor has a basic molecular weight of 14 kd, (2) early pregnancy factor has immunosuppressive activity, (3) polymers of early pregnancy factor also appear to be present in the embryo growth media, and (4) immunosuppressive factors other than early pregnancy factor are also secreted by preimplantation human embryos. Early pregnancy factor and other factor(s) produced by the preimplantation embryo may play a role in suppressing maternal cellular immune responses, thereby preventing maternal rejection of the embryo.

Endocrine control of the immunosuppressive activity of the submandibular gland

Extracts of the submandibular gland (SMG) of rats contain fractions that stimulate the in vitro proliferation of Con A-treated lymphocytes. One of the stimulatory fractions was also shown to induce in vivo immunosuppression in rats and mice in several experimental models. Since many other biologically active factors of the SMG had been found to be hormone dependent, we investigated the effects on the immunosuppressive factor of hypophysectomy (Hx) and of hormonal reconstitution in male Fischer rats. Hx induced a marked atrophy of the SMG together with an almost complete disappearance of both the in vitro lymphocyte-stimulating activity and the in vivo immunosuppressive activity, the latter assayed with the contact sensitivity reaction in mice. The treatment of the Hx rats with pituitary hormones demonstrated that prolactin (PRL), thyroid stimulating hormone (TSH), and luteinizing hormone (LH) induced a significant reconstitution of these biological activities, growth hormone led to the recovery of the lymphocyte-stimulating activity but not of the immunosuppressive activity, while follicle-stimulating hormone, and adrenocorticotropic hormone did not induce any recovery of these biological activities. In view of the positive results obtained with TSH and LH further experiments were done to compare the effects of thyroid and sex hormones with those of PRL. The results demonstrated that testosterone and thyroid hormones induced significant recovery of the lymphocyte-stimulating and the immunosuppressive activity. The combination of these two hormones with PRL produced the most effective results. On the other hand, estrogens and progesterone had no significant effects. These results confirm the effectiveness of androgens and thyroid hormones in stimulating the production of biologically active factors by the SMG. Moreover, they demonstrate that PRL, a hormone not previously considered to increase the activity of the SMG, stimulates the production of immunoregulatory factors in Hx animals.

Detection of nonspecific cytotoxicity in graft-versus-host reaction as a function of target cell type

Abstract The cytotoxic activity of spleen cells from mice undergoing graft-versus-host (GVH) reaction on 51 Cr-labeled target cells was studied under in vitro conditions. Among normal tissues used as target cells, skin fibroblasts proved to be most sensitive to the nonspecific cytotoxic effects of spleen cells from mice undergoing GVH reaction, whereas kidney cells or macrophages were insensitive to these nonspecific cytotoxic effects. Of the two murine neoplastic target cells used, Sarcoma 1 cells were susceptible to these nonspecific cytotoxic effects whereas mastocyoma cells were resistant. However, the target cells which were insensitive to the nonspecific cytolytic effects, were lysed specifically by the spleen cells from animals specifically sensitized. Therefore, both specific and nonspecific cytotoxic effects of spleen cells from mice undergoing GVH reaction could be detected with appropriate targets. These results provide a basis for reconciliation of several apparently contradictory results, reported in the literature, concerning the specificity of the cytotoxic effects of specifically sensitized lymphocytes.

In vitro lysis of tumor cells by guinea pig lymphoid cells sensitized to heterologous gamma globulins

Abstract Lymphoid cells from guinea pigs sensitized to a state of delayed hypersensitivity to mouse or rabbit globulins induced lysis of mouse sarcoma I cells, when these cells were coated with the corresponding globulins in the form of anti-sarcoma I antibodies. Similar lysis of target cells was induced by immune lymphoid cells pretreated with the sensitizing antigen, or in the presence of free antigen in the medium containing immune and target cells. The cytotoxic effect was immunologically specific with respect to the antigens used for induction of delayed hypersensitivity but was nonspecific with respect to the target cells. It is suggested that the mechanism of lysis involves two steps: (i) activation of the sensitized cells on interaction with the specific antigen, and (ii) lysis of target cells on contact with the activated cells. No soluble cytotoxic mediators were detected.

Nonspecific cytotoxicity in graft-versus-host reactions.

SUMMARY Under in vitro conditions, spleen cells from Fx hybrid mice undergoing graft-versus-host (GVH) reactions exerted a nonspecific cytotoxic effect upon target cells of syngeneic, allogeneic, or xenogeneic genotype to the parental strain. The cytotoxic effect was dependent on the intensity of GVH reactions and necessitated direct contact between target cells and metabolically active spleen cells; no lysis could be induced with the cell-free supernatant of cultures of these spleen cells

Immunoregulatory Effects of Glandular Kallikrein from the Salivary Submandibular Gland of Rats

A protein of 40 kD molecular weight was isolated from the salivary submandibular glands of male rats. The protein catalyzed the hydrolysis of alpha-N-benzoyl-L-arginine ethyl ester. This esterase activity was inhibitable with the protease inhibitor aprotinin. The sequence of the first 25 amino acids of this protein was identical to that of rat glandular kallikrein (rGK). When added to cultures of murine lymph node cells suboptimally stimulated with the T cell mitogen concanavalin A, rGK markedly stimulated the proliferative activity of these cells. When injected into mice, rGK suppressed the contact sensitivity response to picryl chloride, a form of delayed-type hypersensitivity. Similar in vitro and in vivo effects were induced with GK from porcine pancreas (pGK). Moreover, the aforementioned in vitro and in vivo effects were abolished by aprotinin either added to the tissue culture medium or injected into the animals immediately before rGK or pGK. This demonstrates that the enzymatic activity of rGK and pGK is important for the induction of immunoregulatory effects. These results suggest that rGK is a systemic immunoregulatory enzyme with immunosuppressive potential. GK is the first example for systemic immunoregulation by an enzyme, the secretion of which is under neuroendocrine control.

Mechanisms of BCG action

SummaryDonor mice were treated IV with BCG and after various time intervals the spleens from these animals were injected into syngeneic recipients which were simultaneously challenged with an allogeneic tumour. The spleen cells from the BCG-treated donors, but not untreated donors, conferred on the recipients an ability to induce a potentiated CMC reaction against the tumour. The transference of BCG-induced potentiating activity could not be explained by the transference of viable BCG organisms, but was mediated by a cell that was anti-Thy.1-sensitive, silica-resistant, plastic-nonadherent, and nylon wool-adherent, and was sensitive in vivo to anti-thymocyte serum but resistant to hydrocortisone. By the use of congenic strains of mice that differed at the Thy.1 allele, it was shown that the cells responsible were not precursors of the cytotoxic lymphocytes but were cells that produced an amplification of the response of the recipient hosts precursor cytotoxic T cells.

In Vivo Destruction of Tumor Cells by an Indirect Cell-Mediated Immune Mechanism

Polyoma cells coated with anti-tumor rabbit antibodies were administered in a lethal dose to C57BL/6J mice. The growth of the tumor cells was partially or completely inhibited in vivo by syngeneic lymphoid cells sensitized to rabbit immunoglobulins. The phenomenon was immunologically specific.