Hypophysectomy and neurointermediate pituitary lobectomy decrease humoral immune responses to T-independent and T-dependent antigens.

In rats, hypophysectomy (HYPOX) or neurointermediate pituitary lobectomy (NIL) reduce humoral and cell-mediated immune responses. However, to our knowledge, the differences in the effects of anterior versus posterior pituitary hormones on the immune responses have not been studied to date. We compared in rats, the effects of sham surgery (SHAM), HYPOX, and NIL on humoral immune responses to T cell-independent (TI) type 1 antigen DNP-LPS and to TI type 2 antigen DNP-FICOLL, as well as to T cell-dependent (TD) antigens ovalbumin (OVA) and bovine serum albumin (BSA). The results showed that: (1) both HYPOX and NIL induced a similar and significant decrease in IgM responses towards TI-1 antigens, (2) NIL but not HYPOX induced a decreased IgM response to TI-2 antigens, and (3) both HYPOX and NIL induced similar and significant decrease in IgG responses to TI-2 antigens. Compared with the SHAM group, IgM responses to both TD antigens did not change in HYPOX and NIL animals, whereas the IgG responses to OVA and BSA significantly decreased in HYPOX and NIL animals. These results indicate that hormones of the anterior and posterior pituitary play their own role in the regulation of humoral immune responses.

Hypophysectomy and neurointermediate pituitary lobectomy decrease humoral immune responses to T-independent and T-dependent antigens

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In rats, hypophysectomy (HYPOX) or neurointermediate pituitary lobectomy (NIL) reduce humoral and cell-mediated immune responses. However, to our knowledge, the differences in the effects of anterior versus posterior pituitary hormones on the immune responses have not been studied to date. We compared in rats, the effects of sham surgery (SHAM), HYPOX, and NIL on humoral immune responses to T cell-independent (TI) type 1 antigen DNP-LPS and to TI type 2 antigen DNP-FICOLL, as well as to T cell-dependent (TD) antigens ovalbumin (OVA) and bovine serum albumin(BSA). The results showed that: (1) both HYPOX and NIL induced a similar and significant decrease in IgM responses towards TI-1 antigens, (2) NIL but not HYPOX induced a decreased IgM response to TI-2 antigens, and (3) both HYPOX and NIL induced similar and significant decrease in IgG responses to TI-2 antigens. Compared with the SHAM group, IgM responses to both TD antigens did not change in HYPOX and NIL animals, whereas the IgG responses to OVA and BSA significantly decreased in HYPOX and NIL animals. These results indicate that hormones of the anterior and posterior pituitary play their own role in the regulation of humoral immune responses (AU)

The thymus and the acute phase response.

The thymus is a primary lymphoid organ with both endocrine and immune functions. There is a large body of evidence indicating the existence of a complex neuroendocrine control of the thymus physiology. This is supported by the historic observation that the thymus becomes involuted during the response to stress. The thymus is dramatically affected by the acute phase response (APR), a systemic reaction to tissue injury and/or infection accompanied by profound neuroendocrine and metabolic changes. The APR comprises alterations in behavior, body temperature, and production and release of cytokines, particularly interleukin (IL)-1, IL-6 and TNFalpha, and glucocorticoids (GCs) and is characterized by suddenly increased production of so-called acute phase proteins (APPs). The stimulation of APR activates the hypothalamic-pituitary-adrenal (HPA) axis, resulting in the suppression of specific immunity, which might serve to protect the organism from adverse immune reactions; the immunostimulatory hormones (e.g., PRL, GH, IGF-1) are suppressed, whereas the production of APPs in the liver is stimulated by IL-6, catecholamines and GCs. The most striking effect of the latter on the immune system is the induction of apoptosis in the thymus. In concert with GCs, elevated levels of catecholamines also selectively suppress immune response mechanisms. APR may be regarded as an emergency response that represents a switch of the host defense from the adaptive immune response which is slow to develop and is commanded by the thymus and T-lymphocytes to a less specific, but more rapid and intense reaction. Here we discuss the immunoregulatory changes during the APR with a special emphasis on the role of thymus in this process.

Antiestrogens affect both pathways of killer cell-mediated oncolysis.

BACKGROUND: Our previous studies indicate that antiestrogenic drugs tamoxifen (TX) and toremifene (TO) augment immune oncolysis induced by various killer cells. The underlying mechanism(s), however, have not been fully elucidated. MATERIALS AND METHODS: Ovarian carcinoma cells freshly isolated from cancer patients and the human erythroleukemia cell line, K562 were used as targets for killer cells and/or the anti-Fas monoclonal antibody, CH-11 in 51Cr release assays. In a number of experiments, extracellular Ca++ was chelated by EGTA/MgCl2 to distinguish Ca(++)-dependent perforin/granzyme pathway from Fas/FasL pathway. Fas expression was studied by flow cytometry. RESULTS: Ovarian carcinoma cells were sensitized by antiestrogens towards enhanced cytolysis mediated by autologous cytotoxic lymphocytes. Antiestrogens also significantly augmented the killing of ovarian carcinoma cells triggered by anti-Fas monoclonal antibody. Flow cytometry analyses showed an upregulation of Fas (CD 95/Apo-1) upon TX or TO treatment in a number of cases. By contrast, antiestrogen treatment did not induce Fas expression in the Fas-negative K562 cells; yet, natural killer cell-mediated cytotoxicity against K562 was augmented by antiestrogens and maximal lysis was achieved when both target and effector cells were treated. The presence of Ca++ chelator (EGTA/MgCl2) in the assay abrogated killing of K562 and its antiestrogen--mediated augmentation. This indicates the involvement of the perforin/granzyme pathway. CONCLUSION: Antiestrogens can influence both Fas/FasL and perforin/granzyme pathways of killer cell--mediated oncolysis.

Antiestrogens sensitize human ovarian and lung carcinomas for lysis by autologous killer cells.

BACKGROUND: The antiestrogens tamoxifen (TX) and toremifene (TO) were shown previously to enhance the lysis of target cells by natural killer cells (NK), lymphokine activated killer (LAK) cells, and by cytotoxic T lymphocytes (CTL). MATERIALS AND METHODS: CTL were cultured from lung cancer tissue and from ascites fluid of ovarian carcinoma patients with the aid of human recombinant interleukin-2 (hrIL-2). The target, effector or both cell populations were pretreated by TX, TO and/or with human recombinant interferon-alpha (IFN-alpha). RESULTS: Significant enhancement of cytotoxicity occurred when the tumor targets or both the target and effector cells were treated with TX, TO or when these drugs were used in combination with IFN-alpha. The lytic activity of CTL cultured from draining lymph nodes of lung cancer patients, was also observed after similar treatment. The lytic effect of autologous LAK cells derived from peripheral blood was increased to a lesser extent, which could be amplified by additional treatment with IFN-alpha. CONCLUSIONS: The antiestrogens TX and TO and IFN-alpha enhance the lysis of autologous tumor cells by CTL and LAK effectors.

Suppression of lymphocyte mitogenesis by tamoxifen: studies on protein kinase C, calmodulin and calcium.

The effect of tamoxifen (TX; 1.0 microM) on the mitogenic response of rat lymphocytes was compared with the effect of drugs that are known to act on protein kinase C (PKC), calmodulin (CM), and calcium (Ca(2+)). The calcium ionophore A23187 (0.2 microM) was mitogenic on its own which was not influenced by TX. The agents modulating PKC or CM (phorbol-myristate-13-acetate; R24571, chlorpromazine) influenced mitogenesis differently than did TX. General inhibition of lymphocyte proliferation was seen with the Ca(2+) antagonist agents (EGTA, TMB-8) as with TX. The antiproliferative effect of TX was partially reversed by the increase of Ca(2+) in the culture medium when T cell mitogens were used, but not in the case of lipid A, a B lymphocyte mitogen. However, the concanavalin A-induced Ca(2+) influx was further elevated by TX which differed from the effect of the Ca(2+) channel-blocking agent verapamil. The results suggest that TX resets the threshold stimulus necessary for mitogenesis and is completely reversible.

Natural immunity and neuroimmune host defense.

Innate resistance is mediated by non-immune defense and by natural immunity. Non-immune defense includes diverse mechanisms (e.g., physico-chemical defense by bile acids). Natural killer (NK) cells, gamma delta T lymphocytes and CD5+ B lymphocytes are key mediators of natural immunity. These cells utilize germ-line coded receptors that recognize highly conserved, homologous epitopes (homotopes). Typically, it is not the antigen, but cytokines and hormones that regulate the level of NK-mediated cytotoxicity. These include interleukin-2, interferons, prolactin and growth hormone. Less is known about gamma delta T lymphocytes. CD5+ B lymphocytes produce germ-line coded antibodies (predominantly IgM) that are polyspecific, and able to recognize a great variety of microorganisms, cancer-cells and self-components. Antigen is not an effective stimulus for natural antibody (NAb), but bacterial lipopolysaccharide (LPS) is. During the acute phase response (febrile illness) the T-cell-regulated adaptive immune response is switched off and natural immune mechanisms are amplified several hundred to a thousand times within 24-48 hours (immunoconversion). This immunoconversion is initiated by immune-derived cytokines, and involves profound neuroendocrine and metabolic changes, all in the interest of host defense. Immune recognition is assured by natural antibodies and by some liver-derived acute phase proteins, such as C-reactive protein or endotoxin-binding protein, the level of which is elevated in the serum. Thus, natural immunity is essential for a first and last line of defense and the neuroendocrine system is an important promoter of this activity.

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.

Neuroimmunoregulation and cancer (review).

It is certain that neuroimmune mechanisms play a role in host defence against cancer. However, this interaction is highly complex and many variations are possible according to the nature of the neoplasms involved. There are indications that adaptive immunity is present in a significant proportion of tumor bearing hosts, and this defence may be boosted by specially designed vaccines and cytokines. Natural immune mediators are also implicated in resistance against tumor development. Here we review the evidence suggesting that hormonal manipulation of the host can result in the elevation of immune defences against cancer. Such manipulation strengthens both the adaptive and natural immune defences of the host, both of which play significant roles. Natural defence mechanisms are boosted by cytokines and hormones during febrile reactions which are now known as the acute phase response. It is suggested that hormonal stimulation of immune mechanisms coupled with the usual immunostimulants already in use may be employed to good advantage for the combination immunotherapy of cancer. Modern molecular biology approaches permit the development of laboratory monitoring procedures which may be used for the prediction and follow-up of therapeutic success.

The stress concept and neuroimmunoregulation in modern biology.

Sixty years ago Hans Selye discovered that the neuroendocrine and immune systems interact during stress. The pathophysiological significance of neuroendocrine-immune interaction during injury has only been recognized recently. Today it is rapidly emerging that, in addition to defense against exogenous pathogenic agents, the immune system plays a key role in host defense against injury. During acute-phase reactions to infection/injury, when there is no time to mount a specific immune response, the neuroimmunoregulatory network suppresses specific immunity while rapidly elevating the production of acute-phase proteins (APP) in the liver. APP recognize microbes and abnormal cells/tissues and activates the immune system nonspecifically to fight infection or injury. There is a remarkable similarity between the stress syndrome as outlined by Selye in 1946 and the acute-phase response as we know it today. Moreover, it is becoming clear that the immune system participates in the normal physiological regulation of the body, which was also recognized by Selye in his later years. Although with much delay, the scientific community is beginning to fully appreciate Selye's ingenious discoveries which were far ahead of his time.

Neurohormonal host defense in endotoxin shock.

Lipopolysaccharide (LPS) of gram-negative bacteria is capable of activating the immune system of higher animals, which may lead to cytokine-induced lethal shock and death. LPS has little toxicity for the frog and fish, but it kills the horseshoe crab instantly by causing intravascular blood coagulation. The response to LPS evolved from simple reactions in lower animals into an intense reaction in mammals that involves a massive immune activation leading to a profound neuroendocrine and metabolic response. This is now known as the acute-phase response (APR). During APR, LPS-binding proteins (LBP) are produced by the liver in rapidly increasing quantities under the influence of interleukin-6, glucocorticoids, and catecholamines. After combination with LPS, LPB is capable of activating monocyte-macrophages and granulocytes via the CD14 surface receptor. Other receptors (CD18, 80-kDa receptor) allow for direct action by LPS of phagocytes, B and T lymphocytes, and other cells. Numerous other acute-phase proteins are produced in the liver, including C-reactive protein, complement components, fibrinogen, enzyme inhibitors, and anti-inflammatory proteins. Similar responses may be stimulated by subtoxic doses of LPS or by detoxified LPS, which manifest in endotoxin tolerance. Tolerant animals and man show increased resistance to LPS, to infections, and to various noxious insults. Infection and various forms of tissue injury are also capable of causing APR. There is much evidence to indicate that APR, which manifests in febrile illness, is an efficient host defense reaction. It is an emergency response in cases where specific immunity fails to protect the host. Therefore, the neuroimmunoregulatory network converts the immune system to a less specific, but rapid and more efficient response, APR. The hypothesis is presented that intestinal LPS serves to amplify the APR in response to various insults, which contribute to host defense, regeneration, and healing.

Pituitary hormones and immune function.

The pituitary gland plays a key role in the regulation of growth, differentiation and function of all cells in the body, including immunocytes. Immune reactions are generated through the proliferation of antigen-specific lymphocyte clones. Growth hormone and prolactin are required for the development of mature lymphocytes and for the maintenance of immunocompetence. These hormones enable lymphocytes to respond to antigen, which is delivered as an adherence signal in the context of major histocompatibility surface molecules of antigen-presenting cells. Numerous other adhesion molecules play a role in the regulation of lymphocyte activation. The activation process is completed by cytokine signalling, after which lymphocyte proliferation, differentiation and functional maturation take place. Interleukins, hormones and growth factors may all function as cytokines. Many lymphocytes exist in the body in a quiescent state, with minimal metabolic activities. These cells are maintained by competence hormones and insulin-like growth factor 1, which are present in the systemic and local environment. Apparently, some steroid hormones, opioid peptides and catecholamines are capable of modulating delivery of the signal from the lymphocyte membrane receptor to the nucleus. Steroid and thyroid hormones control nuclear transcription factors as their receptors, and thus are powerful regulators of lymphocyte signalling at the nuclear level. The bioactive forms of thyroid hormone and of several steroid hormones are generated locally by immunocytes. These important hormonal immunoregulators function both at systemic and local levels. Glucocorticoids are major regulators of cytokine production, and alpha-melanocyte-stimulating hormone functions as a powerful cytokine antagonist. The hormones secreted or regulated by the pituitary gland therefore regulate every level of immune activity, including the competence of lymphocytes to respond to immune/inflammatory stimuli, signal transduction, gene activation, the production and activity of cytokines and other immune effector functions.

Combination therapy of the H2712 murine mammary carcinoma with cytotoxic T lymphocytes and anti-estrogens.

BACKGROUND: The triphenylethylene antiestrogenic agents, tamoxifen (TX) and toremifene (TO), are currently being used for the therapy of estrogen dependent breast carcinomas and for some other estrogen receptor positive tumors. Some observations indicate that these drugs may have a beneficial effect on estrogen receptor negative tumors as well. MATERIALS AND METHODS: The H2712 mammary carcinoma of C3H/HeJ mice was studied in combination immunotherapy experiments using cytotoxic T lymphocytes (CTL) and TX or TO. The effect of TX and TO on the in vitro lysis of H2712 cells by CTL was also investigated. Finally, the H2712 cells were examined for the presence of estrogen receptors. RESULTS: Both TX and TO potentiated the lysis of H2712 cells by CTL in vitro, and exerted a growth inhibitory and therapeutic effect on H2712 mammary carcinomas in vivo. The therapeutic effect of CTL isolated from tumor bearing mice was improved on H2712 carcinomas when the animals were also treated orally by TX or TO. Using the dextran-coated charcoal assay, H2712 cells were found to be negative for classical estrogen receptors. CONCLUSIONS: These results indicate that the anti-estrogens, TX and TO, have the ability to suppress the growth of the estrogen receptor negative mammary carcinoma and to amplify target cell lysis by tumor-reactive CTL. By this mechanism these drugs enhance host immunity to an estrogen receptor negative tumor.

Combination immunotherapy of the P815 murine mastocytoma with killer cells, IL-2 and anti-estrogens.

BACKGROUND: Lymphokine activated killer (LAK) cells, cytotoxic T lymphocytes (CTL) and interleukin-2 (IL-2) all are being tested in cancer immunotherapy with modest success. The anti-estrogenic drug, toremifene (T0), was found earlier to amplify cancer immunotherapy with killer cells in mice. Here T0 is examined in combination with CTL and IL-2 in immunotherapy experiments. MATERIALS AND METHODS: The P815 mastocytoma of DBA/2 mice was treated with combinations of CTL, LAK cells and T0 and combinations of CTL, IL-2 and T0 along with control groups. Tumor growth rate and mortality has been recorded. RESULTS: Combined treatment with CTL and LAK cells cured 25% of tumor bearing animals, as did treatment with tamoxifen (TX) or T0 alone. When killer cells were given in conjunction with anti-estrogens the cure rate was 75% with both TX and T0. Human recombinant IL-2 significantly inhibited tumor growth but no cures occurred. CTL alone cured 25% of the animals. When CTL and IL-2 treatment was given jointly with T0 75% of tumor bearing animals were cured. CONCLUSIONS: The results indicate that treatment with anti-estrogens increased the efficiency of immunotherapy by killer cells. This was true also when CTL therapy was supplemented with IL-2 treatment.

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.

Anti-estrogens potentiate the immunotherapy of the P815 murine mastocytoma by cytotoxic T lymphocytes.

Many animal and human tumors are infiltrated with killer cells. Recent studies have shown that the stimulation of such killer cells with interleukin-2 improves their tumor rejecting capacity. In this paper we demonstrate that the anti-estrogens, tamoxifen (TX) and toremifene (TO), enhance host resistance by sensitizing the tumor target to killer cell mediated lysis. The P815 mastocytoma syngeneic to DBA/21 mice was used. Cytotoxic T lymphocytes (CTL) were detected in the spleens of mice 12-14 days after tumor inoculation. In vitro target, effector, or both cell types were treated with either TX (1 microM) or TO (5 microM) for 4 hours prior to cytotoxicity testing by 51Cr release. Mice bearing P815 mastocytomas, 5 mm in diameter, were treated orally with TX or TO and were given CTL isolated from the spleens of tumor bearing donors i.p. Tumor growth, mortality, and immunological memory in cured animals were monitored. Both TX and TO treatment sensitized P815 target cells to lysis by CTL isolated from tumor bearing animals. The transfer of killer cells from the spleens of tumor bearing mice produced tumor suppression in the recipients, which could be enhanced by additional oral treatment by TX or TO. Complete cure was achieved in a significant number of animals, showing partial or complete resistance to a subsequent lethal dose of P815 cells. These experiments indicate that killer cells isolated from mice bearing progressive tumors can have an immunotherapeutic effect in syngeneic tumor bearing recipients and that the antiestrogens, TX and TO, may be used to potentiate the immunotherapy of this tumor.

Immunotherapy of the SL2-5 murine lymphoma with natural killer cells and tamoxifen or toremifene.

It is well established that tamoxifen (TX) has a therapeutic effect on estrogen receptor positive tumors by inhibiting the binding of estradiol to its receptor. However, repeated clinical observations indicate that tamoxifen may also have beneficial effects on estrogen receptor negative tumors. In vitro cytotoxicity experiments were performed with the SL2-5 murine lymphoma using interleukin (IL)-2 activated syngeneic NK cells as effectors with or without TX or TO treatment. The effect of TX or TO (10 mg/kg/day/animal in feed) on the immunotherapy of SL2-5 lymphoma with syngeneic IL-2 activated NK cells was also investigated in syngeneic DBA/2 mice. Assays of SL2-5 cells for estrogen and progesterone receptors were also performed. Both TX and TO enhanced significantly the susceptibility of the SL2-5 lymphoma to lysis by IL-2 activated NK cells in vitro. When TX or TO treatment was combined with NK cell immunotherapy of this tumor, both drugs potentiated significantly tumor regression and cure rate when compared to groups receiving NK therapy alone. This tumor does not express classical receptors for estrogens or progesterone. These results indicate that combination treatment with the antiestrogens, TX and TO, acts synergistically with the immunotherapeutic effect of IL-2 activated NK cells in a syngeneic tumor host system.

Neuroimmune mechanisms in health and disease: 1. Health.

A novel scientific discipline that examines the complex interdependence of the neural, endocrine and immune systems in health and disease has emerged in recent years. In health, the neuroimmunoregulatory network is fundamental to host defence and to the transfer of immunity to offspring; the network also plays important roles in intestinal physiology and in tissue regeneration, healing and reproduction. The proliferation of lymphocytes in primary lymphoid organs (bone marrow, bursa of Fabricius [in birds] and thymus) and in secondary lymphoid organs (spleen, lymph nodes and mucosal lymphoid tissue) depends on prolactin and growth hormone. These hormones allow immune cells to respond to antigen and to soluble mediators, called cytokines. Immune-derived cytokines are capable of inducing fever and of altering neuro-transmitter activity in the brain and hormone secretion by the pituitary gland. The activation of the hypothalamus-pituitary-adrenal axis by cytokines leads to immunosuppression. Lymphoid organs are innervated, and tissue mast cells respond to neurologic stimuli. In general, acetylcholine and substance P exert immunostimulatory and proinflammatory effects, whereas epinephrine and somatostatin are immunosuppressive and anti-inflammatory. In this article, the authors predict that novel approaches to immunomodulation will be possible by altering the level or efficacy of immunoregulatory hormones and neurotransmitters.

Neuroimmune mechanisms in health and disease: 2. Disease.

In the second part of their article on the emerging field of neuroimmunology, the authors present an overview of the role of neuroimmune mechanisms in defence against infectious diseases and in immune disorders. During acute febrile illness, immune-derived cytokines initiate an acute phase response, which is characterized by fever, inactivity, fatigue, anorexia and catabolism. Profound neuroendocrine and metabolic changes take place: acute phase proteins are produced in the liver, bone marrow function and the metabolic activity of leukocytes are greatly increased, and specific immune reactivity is suppressed. Defects in regulatory processes, which are fundamental to immune disorders and inflammatory diseases, may lie in the immune system, the neuro endocrine system or both. Defects in the hypothalamus-pituitary-adrenal axis have been observed in autoimmune and rheumatic diseases, chronic inflammatory disease, chronic fatigue syndrome and fibromyalgia. Prolactin levels are often elevated in patients with systemic lupus erythematosus and other autoimmune diseases, whereas the bioactivity of prolactin is decreased in patients with rheumatoid arthritis. Levels of sex hormones and thyroid hormone are decreased during severe inflammatory disease. Defective neural regulation of inflammation likely plays a pathogenic role in allergy and asthma, in the symmetrical form of rheumatoid arthritis and in gastrointestinal inflammatory disease. A better understanding of neuroimmunoregulation holds the promise of new approaches to the treatment of immune and inflammatory diseases with the use of hormones, neurotransmitters, neuropeptides and drugs that modulate these newly recognized immune regulators.