Robert Rapaport, Mount Sinai Hospital, Diabetes Center,
1200 Fifth Avenue 9, New York, NY 10029, USA

Published by: Elsevier Science
ISBN: 0-444-510516
NeuroImmune Biology: Volume 2: Growth and Lactogenic Hormones

Advisory Board:

B.G. Arnason, Chicago, IL
P.J. Barnes, London, UK
T. Bartfai, La Jolla, CA
L. Bertok, Budapest, Hungary
H.O. Besedovsky, Marburg , Germany
J. Bienenstock, Hamilton, Canada
C.M. Blatteis, Memphis, TN
J. Buckingham, London, UK
C. Chawnshang, Rochester, NY
M. Dardenne, Paris, France
R.C. Gaillard, Lausanne, Switzerland
R. Good, Tampa, FL
R.M. Gorczynski, Toronto, Canada
C. Heijnen, Utrecht, The Netherlands
T. Hori, Fukuoka, Japan
G. Jancso, Szeged, Hungary
M.D. Kendall, Cambridge, UK
E.A. Korneva, St. Petersburg, Russia
K. Kovacs, Toronto, Canada
G. Kunkel, Berlin, Germany
L. Matera, Turin, Italy
D. Nance, Winnipeg, Canada
H. Ovadia, Jerusalem, Israel
C.P. Phelps, Tampa, FL
L.D. Prockop, Tampa, FL
R. Rapaport, New York, NY
S. Reichlin, Tucson, AZ
K. Skwarlo-Sonta, Warsaw, Poland
E.M. Sternberg, Bethesda, MD
D.W. Talmage, Denver, CO
S. Walker, Columbia, MO
A.G. Zapata, Madrid, Spain

Description:

For more than seventy years evidence has accumulated documenting the existence of interaction between growth hormone and the immune system. In the past twenty years there has been a tremendous proliferation of information detailing the function of the growth hormone and insulin-like growth factor axis. A multitude of growth factors and binding proteins have been identified. More and more evidence supporting the important role of the growth hormone - IGF axis in the well functioning of the normal immune system has been documented. Clearly the challenge today is not to prove, but to understand, the neuroimmune regulatory role of growth and lactogenic hormones in its entire complexity.

The ultimate goal of this volume and of all the other volumes of this series is to promote the understanding of the science of Neuroimmune Biology and to ease human suffering.
 

Contents

Foreword: The Neuroimmune Biology of Growth and Lactogenic Hormones.
Istvan  Berczi.

Preface:
Robert Rapaport

List of  Corresponding Authors

I. Introduction

Immunoregulation by Prolactin - An Introduction.
Lina  Matera

II. GLH Biology, Development & Receptors

The Growth Hormone - Insulin-Like Growth Factor - I Axis and Immunity.
Wilson Mejia Naranjo, Myriam Sanchez-Gomez, Derek Le Roith

Reciprocal Interactions between the GH/IGF-1 System and Cytokines.
Fabrizio de Benedetti, Mauro Bozzola

Biological Significance of Insulin-Like Growth Factor Binding Proteins.
Stuart Alan Weinzimer, Pinchas Cohen

The Expression and Function of GH/IGF-I Receptors in the Immune System.
Alfred Tenore, Giuliana Valero

Growth Hormone and Insulin-Like Growth factor-1 Production by Cells of the Immune System.
Douglas Weigent

Potential Applications of Growth Hormone in Promoting Immune Reconstitution.
William J. Murphy, Lisbeth Welniak, Rui Sun

Signal Transduction by PRL Receptors.
Li-yuan Yu-Lee

Signal Transduction and Modulation of Gene Expression by Prolactin in Human Leukocytes.
R. Hooghe, S. de Vos, Z. Dogusan, E.L. Hooghe-Peters

Regulation of PRL Release by Cytokines and Immunomodifiers: Interrelationship between Leptin and Prolactin Secretion. Functional Implications.
Oreste Gualillo, Eduardo Caminos, Ruben Nogueiras, Celia Pombo, Fransica Lago, Felipe F. Casanueva, Carlos Diéguez

Prolactin Expression in the Immune Cells.
Ron  Kooijman, Sarah Gerlo

III. Hemopoiesis and Development

Prolactin as a Promoter of Growth and Differentiation of Hemopoietic Cells.
Graziella Bellone

Growth Hormone/Insulin-Like Growth Factors and Hematopoiesis.
Robert. Moghaddas, Robert Rapaport

Uteroplacental prolactin Family: Immunological Regulators of Viviparity.
Rupasi Ain, Heiner Müller, Namita Sahgal, Guoli Dai, Michael J. Soares

IV. GLH and the Immune Response

Effect of Prolactin on Natural Killer and MHC-restricted :Cytotoxic Cells.
Lina Matera, Stefano Buttiglieri, Francesco Moro, Massimo Geuna

In Vivo Changes of PRL Levels During the T-cell Dependent Immune Response.
Carolina Perez Castro, Marcelo Páez Pereda, Johannes M.H.M. Reul, Günther K. Stalla, Florian Holsboer, Eduardo Arzt

Prolactin Regulates Macrophage and NK Cell Mediated Inflammation and Cytotoxic Response Against Tumor.
Uptala Chattopadhyay, Ratna Biswas

V. GLH and Disease

Acromegaly and Immune Function.
Annamaria. Colao, Diego Ferone, Paolo Marzullo, Gaetano Lombardi

Growth Hormone and Insulin-Like Growth Factor-1 in Human Immunodeficiency Virus Infection.
Mitchell E. Geffner

Human prolactin as an Immunohematopoietic Factor: Implications for the Clinic.
Susan.M. Richards

Effectiveness of Bromocriptine in the Treatment of Autoimmune Diseases.
Sara E. Walker

The pathogenic Role of prolactin in Patients with Rheumatoid Arthritis.
Noboru Suzuki

(Article reprint used with permission, NIB 2002;2:v-xiv)
FOREW0RD:The Neuroimmune Biology of Growth and Lactogenic  Hormones.

     Growth hormone (GH) has long been shown in animals to stimulate immune and inflammatory reactions. However, clinicians did not find immune abnormalities in pituitary dwarf individuals, which raised serious doubts about the role of GH in immune function [1,2]. To this date it is difficult to demonstrate immune alterations in children after GH therapy, although transient responses can be demonstrated. However,  in vitro observations with human lymphocytes indicate the role of GH in immunoregulation [3].

     For the immunoregulatory role of prolactin (PRL) the first decisive evidence was obtained in hypophysectomized (Hypox) rats, which are immunodeficient [4]. Replacement doses of PRL or GH completely restored the immune reactivity of Hypox animals. Moreover, treatment with the dopaminergic drug, bromocriptine, which inhibits pituitary PRL secretion, was as immunosuppressive as was Hypox. Again the immune response could be restored with either GH or PRL treatment [5-12]. Subsequently numerous observations confirmed the immunoregulatory potential of PRL and GH, as attested for in this volume.

     Although much less studied, the evidence available clearly indicates that placental lactogenic hormones (PL) also have the potential of regulating the immune system [7,13-15].

SOME TIMELY QUESTIONS AND ANSWERS.

Why pituitary dwarf individuals are immunocompetent?

     Pituitary dwarfs have normal serum PRL levels [16]. Animal experiments showed that PRL is able to maintain immune function in the absence of GH [6-8,11]. On this basis it is reasonable to suggest that PRL is responsible for the maintenance of immunocompetence in dwarf people as well.

Snell dwarf mice are deficient in both PRL and GH, yet show immunocompetence, why?

     These mice are deficient of the pituitary transcription factor, Pit-1, which controls the production of GH, PRL and of thyroid stimulating hormone (TSH) secretion. In the recent literature these animals have often been presented as lacking completely pituitary GH and PRL secretion. However, low serum level of GH and PRL was detectable in these animals by radioimmunoassay [17-19]. Moreover, humans with Pit-1 mutations have subnormal levels of GH, PRL and TSH, and are not negative [20]. It was also shown that Snell dwarf mice produced less lymphocyte-derived PRL (LPRL) than did their normal littermates. LPRL could be restored to normal by thyroxin treatment of lymphocytes  in vitro . The production of placental lactogen was normal [21]. Therefore, it appears that Pit-1 deficient mice and humans do in fact, have sufficient pituitary hormone levels, which permit survival and immune function. Clearly, the joint and complete deficiency of pituitary GH and PRL has not been demonstrated to date in man or in animals. This point is further illustrated by the observation that Hypox rats are able to survive for 6-8 months because of the presence of residual PRL in their serum. If this residual PRL is neutralized by antibodies, the animals will perish within a few weeks time [22].

Mice that lack PRL or IGF-I function survive and are immunocompetent, why?

     Knockout mice, lacking either PRL or its receptor (PRLR), or IGF-I are immunocompetent. It was interpreted, therefore, that these hormones are not obligate immunoregulators, but rather, affect immune reactions as anabolic and stress modulating agents [23-25]. In actual fact the data obtained in knockout mice is a powerful confirmation of the original observations that growth and lactogenic hormones (GLH) show redundancy in the maintenance of immunocompetence [7-11]. Today a compelling body of experimental evidence, which is presented in this volume, indicates that indeed this is the case. Clearly, immune function, as many other functions in the body, are maintained by multiple genes that show redundancy [26].

      Growth hormone and PRL belong to the type-I cytokine family [27]. Functional overlap and redundancy is the rule for type I cytokines (and for other cytokines as well) in the immune system. The receptor for type I cytokines consists of a ligand specific chain and of a shared signal transducing chain. For instance in the first group, where IL-2, -4, -7, -9 and -15 belong, there is a common gamma chain , for the second group (IL3, -5 and GM-CSF) it is called the common beta chain  and for the third group (Il-6, -11, oncostatin M, leukemia inhibitory factor, ciliary neurotropic factor and cardiotrophin-1) the common chain is glycoprotein 130. Signal transduction is possible only if the ligand binding and the signal transducing chains are crosslinked by the specific cytokine. Knockout experiments in this system showed that the elimination of specific cytokines or their specific receptor chains produced minimal if any abnormalities. However, knocking out the shared signal transducing common gamma chain resulted in severe combined immunodeficiency [27,28]. These observations collectively indicate that  type I cytokines are indispensable as a group for normal immune function. Apparently there is enough redundancy in this group to compensate for the lack of any particular cytokine.

     Prolactin and growth hormone do not share receptor chains with any of the above cytokines. However, human GH and other primate GH are known to act on PRL receptors and to exert lactogenic activity in many species [29]. Similarly, IGF-I, IGF-II and insulin show functional overlap [13]. These facts indicate that  functional redundancy exists within GLH hormones, which explains why the disabling of a single gene is of no consequence for immune function.

     The major signal transduction pathway, which involves the Janus kinase (JAK) and signal transducers and activators of transcription (STAT) nuclear regulatory factors, is shared between cytokines and growth and lactogenic hormones. STAT knockout mice show severe developmental and immune deficiencies [14,27,28,30]. This emphasizes the significance of this signal transduction pathway in immune development and function [31,32].

     The evidence, that has accumulated to date, indicates that  GLH are indispensable as a group for normal development and bodily functions, including immune function [14,15, 22, 24, 31, 33, 54] . Because the JAK-STAT transcription pathway of PRL and GH are shared with interleukins and hemopoietic growth factors [14,27,29], some regard PRL and GH as members of the hemopoietic cytokine family. However, GLH have a much wider spectrum of biological activity than any of the type I cytokines. A functional overlap with these cytokines could simply indicate the capacity of GLH hormones to maintain the hemopoietic and immune systems at times when cytokines are in short supply as well as to boost immune activity in situations of emergency.

     Female mice that lack PRL or do not respond to it, do not reproduce [23-25]. In this context, one must not forget that without normal immune function reproduction is not possible. The immune system is involved in the function of the gonads, in conception, in the normal development of the fetus and it plays a role in the normal function of the mammary gland. Milk plays a very important role in the transfer of maternal antibodies and of other immune factors and PRL itself to the fetus. There is evidence to indicate that PRL is important for the immunological function of the mammary gland [15, 33-37]. Therefore, the immunoregulatory function of PRL may be of special importance in the female reproductive compartment.

Seriously ill patients got worse after treatment with GH, why?

     In patients with acute phase response (APR) the GH-IGF-I axis is suppressed. This observation prompted several clinical trials with GH, which were aimed at restoring this axis in the hope of preventing the severe catabolic state and to improve immunocompetence in the interest of increased survival. However, so far this hope did not materialize. In fact a controlled clinical trial showed that GH treatment of severely ill patients significantly elevated the proportion that did not survive [38]. Deaths attributed to " septic shock or uncontrolled infection" occurred nearly four times more commonly in GH treated patients compared to placebo receiving patients. Although no data were given regarding immune parameters, the authors suggested that alterations in immune functions could have contributed to these fatalities.

     Critical illness elicits a highly coordinated and powerful acute phase reaction, whereby the immune system is switched from the adaptive mode of response to the amplification of natural immune mechanisms. The acute phase response is characterized by profound elevations of interleukin-1, interleukin-6 and tumor necrosis factor-alpha,(TNF-alpha), which induce complex neuroendocrine and metabolic alterations. The hypothalamic - pituitary- adrenal axis is activated, whereas the serum levels of growth hormone, insulin-like growth factor and prolactin are suppressed. Tri-iodothyronine is also diminished (sick euthyroid syndrome). The increased serum level of cytokines and the array of neuroendocrine changes lead to fever, catabolism and to the suppression of the T lymphocyte-dependent adaptive immune system. At the same time natural immune mechanisms are amplified. There is a rapid rise in serum natural antibodies and liver-derived acute-phase proteins such as endotoxin-binding protein and C-reactive protein. These antibodies and acute phase proteins have the capacity to recognize homologous crossreactive epitopes (homotopes) on microbes and on altered self components in a polyspecific fashion and activate immune defense mechanisms after combining with the respective homotope. Host defenses against toxins and other noxious agents are also increased during the acute phase response [39-41].

     The acute phase response is a massive neuroimmune and metabolic response that mobilizes all the resources of the body in the interest of host defence and survival. The findings of Takala and co-workers [38] suggest strongly that the suppression of the GH - IGF-I axis in APR is required for intense catabolism to take place. A rapid release of nutrients and of energy is necessary under these conditions in order to support maximally the defence system of the body, that includes the hypothalamus - pituitary - adrenal axis, the sympathetic nerves system, the bone marrow, CD5+ B lymphocytes, leukocytes and the liver [39-41]. The adaptive immune system is controlled by thymus-derived (T) lymphocytes and needs several days to a week for an effective response. During APR no time is available for an adaptive immune reaction, and therefore this system is shut down, primarily by the cytokine and endocrine alterations that take place. The thymus and T cell function is heavily dependent on the GH/PRL - IGF-I axis and it is suppressed profoundly by the elevated levels of glucocorticoids and cathecolamines [39-41]. Recent observations showed that GH inhibits the production of acute phase proteins in rats with burn injury and in human hepatocytes [42-43]. These findings strongly support the above hypothesis.

     One may argue that the most efficient way to fuel the intensive systemic effort for survival in APR is by the rapid breakdown of bodily tissues. GH is a powerful anabolic hormone, which supports the T lymphocyte dependent immune system, and acts as antagonist of the HPA axis that promotes APR [6,8,11,39-41,44]. The results of this controlled trial supports the hypothesis that the inhibition of the HPA axis and of catabolism by GH treatment in APR hampers the bodies defence mechanisms, which may have fatal consequences.

What is the role of GLH in the neuroimmune regulatory network?

    Current evidence indicates that GLH is required for the normal growth and development of embryos as well as for the development of the immune system and the maintenance of immunocompetence. Clearly, GLH supports any adaptive immune function and natural immunity under physiological conditions. Lymphocyte precursors do not have receptors for antigen or cytokines and for this reason must rely on physiological mediators for survival and differentiation. Even after full differentiation, naïve lymphocytes remain small and do not synthesise, neither do they respond to immune-derived cytokines. In the absence of antigenic stimulation these cells must rely on physiological systemic mediators to survive. The thymus and other lymphoid organs lose cellularity and weight in Hypox rats, which also show a profound immunosuppresion. The weight of lymphoid organs and immune reactivity can be normalized in Hypox animals by replacement doses of either PRL or GH [45]. The situation is similar in old animals to some extent, although full immune restoration by GH treatment was not possible [46]. Both GH and PRL are capable of maintaining immunocompetence, which is antagonized by the hypothalamus-pituitary adrenal axis [44]. This enables the pituitary gland to exert a true regulatory effect on the immune system. Clearly, the pituitary gland does not only maintain immunocompetence, but also, is capable of fine tuning the level of reactivity and plays a fundamental role in the induction of immunoconversion during APR [5,6,9, 41,45].

     There is compelling evidence to indicate that after activation by antigen or mitogen lymphocytes produce their own PRL and/or GH. This makes the rapid proliferation required for an immune response feasible [48-53]. This situation is similar to the development of the embryo, where placental lactogenic hormones make it possible for the embryo to grow at a very rapid rate. The production of placental GLH is independent from the pituitary gland and is controlled by " placental" promoters. This allows these hormones to override the regulatory power of the maternal pituitary gland during pregnancy in the interest of assuring the proper development of the fetus. Therefore, while conception is clearly dependent on normal pituitary function, the fetus becomes independent from such influence [54].

     Interestingly placental promoter was found also in association with the lymphocyte PRL gene [55]. However, Pit-1 was also detected in lymphocytes [56]. This suggests that once the lymphocyte PRL gene is activated, pituitary PRL is no longer required for lymphocyte growth or function. Once the immune response is over, most of the activated lymphocytes will undergo apoptosis, which is governed by a complex mechanism that involves the delivery of death signals, primarily by the Fas-FasL system. However, a specialize subset called memory cells, will survive [57,58].

     We observed years ago that the primary antibody response is fully pituitary dependent, whereas the secondary response shows only partial dependence. Actually, when the rats were immunized first, hypohysectomized and immunized again, they produced antibodies in response to the second stimulus, which was of similar magnitude to the primary response [6]. These results suggest that memory cells maintained their reactivity after Hypox, but the rapid recruitment of naïve lymphocytes, which occurs in normal animals, could not take place.

     The mechanism(s) for the long term survival and self-renewal capacity of memory B and T lymphocytes is not understood. It was hypothesised that memory B lymphocytes are stimulated by idiotypes, which are unique determinants of antigen receptors [59]. Major histocompatibility antigens presenting self peptides were suggested to fulfill a stimulatory role for memory T lymphocytes [60]. The role of cytokines in T cell longevity is also recognized and IL-15 was claimed to be necessary for CD8+ memory cells [61]. T lymphocyte apoptosis is inhibited by interferon-alpha (IFN-alpha) and IFN-beta and were proposed to play a role in memory cell survival. These cytokines are able to maintain T cells without an antigenic stimulus [62]. Recently Cho and co-workers [63.] demonstrated that in recombinase deficient (RAG-1 -/-) mice, which are lymphopenic, naïve T lymphocytes undergo "homeostasis-stimulated" proliferation, which is MHC restricted, and develop into memory cells in the absence of antigenic stimulation. These cells acquire the phenotypic and functional characteristics of antigen-induced memory CD8+ T cells and lyse target cells directly and respond to lower doses of antigen than naïve cells and secrete IFN-gamma faster upon restimulation. Interleukin-2 or co-stimulation by CD28 are not required and effector cells are not formed during this homeostatic differentiation. These findings indicate that memory T cells may be generated and maintained under the influence of physiological immunoregulatory mechanisms, in the complete absence of immune stimulation by antigen.

     Immature thymocytes of rodents are killed by glucocorticoids, whereas mature thymocytes are saved. The helper, suppressor and killer functions of T lymphocytes and the production of interleukins by them are all inhibited by glucocorticoids. In contrast, the function of memory cells and of cells mediating the graft-versus-host reaction is not inhibited by glucocorticoids [64]. Prolactin and GH antagonize the immunosuppressive effects of the ACTH-adrenal axis [6,8,11]. Taking all the evidence in consideration, one may suggest that naive T cells are maintained in the absence of antigenic stimulation by pituitary GLH, whereas memory T cells are autonomous and survive and resist glucocorticoids, most likely because they produce autocrine GLH and cytokines that enable these cells to survive and to resist adverse conditions, such as the APR.

     This pattern of obtaining gradual independence assures maximal host defence while the maturation and selection process of lymphocytes in the thymus and bone marrow is tightly controlled by the neuroimmune regulatory system. Pituitary GLH is important for the development of lymphocytes and of the maintenance of mature  naïve cells in a state of immunocompetence [22,45]. It is likely that after activation lymphocyte-derived GLH gradually assumes a prominent role in the maintenance of lymphocyte function. Finally, it appears that memory cells rely on autocrine GLH for long term survival and function. This is to be substantiated further experimentally.

3.  FROM BENCH TO BEDSIDE

     The goal of this volume is to present the current evidence for the role of growth and lactogenic hormones in the neuroimmune regulatory system. The evidence presented is compelling and shows that all the requirements for proven biological significance have been fulfilled. Receptors for GLH on cells of the immune system have been characterized, signal transduction pathways have been identified and are being characterized, and the immunoregulatory activity of GLH has been demonstrated in various species, including man. It is also clear that both PRL and GH are produced within the immune system by activated cells. Placental, pituitary and tissue derived GLH hormones all play a role in neuroimmunoregulation. This redundancy serves well the adaptability and versatility of the neuroimmune regulatory network as well as of immune function.

     Finally, the therapeutic use and manipulation of GLH is currently underway for the treatment/correction of various human conditions. Therefore, the ultimate criterion for the success of scientific research, i.e the application of knowledge obtained on the laboratory bench at the bedside is being fulfilled. It is very rewarding to witness one's initial research efforts to develop and reach this critical stage. No reasonable arguments can be raised any more in the face of this evidence against the fundamental role of growth and lactogenic hormones in immunoregulation. Clearly the challenge today is not to prove, but to understand, the neuroimmune regulatory role of GLH in its entire complexity.

4. THE FUTURE

    The realization that a third systemic regulator, the immune system, is included in homeostatic and in allostatic regulation to form the Neuroimmune regulatory network, provides new foundation to Biology. This network is immensely complex and powerful and is involved in both physiological (homeostatic) and pathophysiological (allostatic) regulation. Indeed the entire biological cycle from conception till death of the individual is subject to this regulatory system. It is also clear that the defects and abnormalities of this system is the underlying cause for many diseases that include neural conditions, endocrine and metabolic diseases immune abnormalities (immunodeficiency, hypersensitivity conditions and autoimmune diseases, etc) and others [65]. A better understanding of neuroimmunoregulation is obligatory for obtaining new insights into the pathogenesis of these conditions and for the development of more rational approaches to treatment. The ultimate goal of this volume and of all the other volumes of this series is to promote the understanding of the science and to ease human suffering.

ACKNOWLEDGEMENT:

I thank Dr. Robert Rapaport, who has contributed significantly to the interpretation of the findings in critically ill patients after GH treatment. Many other colleagues contributed over the years to experimentation and to the development of the viewpoints expressed in this article. Notably, I owe special thanks to Drs Eva Nagy, Edris Sabbadini, Robert Shiu, Henry Friesen, Robert Matusik, Richard Warrington, Kalman Kovacs and Sylvia Asa.

The experimental work discussed here was supported in part by MRC of Canada and the Arthritis Society of Canada.
 
 

Elsevier Book Winners - BMA Awards 2003

Growth and Lactogenic Hormones, Volume 2 of the Neuroimmune Biology book series received a Highly Commended Award in the Basic and Clinical Sciences category of the British Medical Association's 2003 book competition.