The amoebocytic corpuscles in the circulating fluid of the lamelli-branches, Indonaia caerulia and Parreysia (Parreysia) favidens.

The circulating amoebocytes of the freshwater mussels, Indonaia caerulia and Parreysia favidens have been studied. The total number of amoebocytes is low and variable, and the individual to individual variation in total counts is particularly significant. The amoebocytes are of 3 main types: Acidophils, Large Basophils and Small Basophils. Acidophils contain large acidophilic granules and basophils fine basophilic granules within the cytoplasm. Acidophils are the largest and small basophils the smallest. The greater volume of the cell is occupied by cytoplasm in acidophils and large basophils and by the nucleus in small basophils. Large basophils are the most and small basophils the least abundant. Amoebocytes clump together by means of filipodia. Large basophils possess these protoplasmic processes in the greatest abundance, and partake most actively and in largest numbers in clumping; while small basophils lack filipodia and play an absolutely passive role. Clumping progressively becomes more extensive with passage of time following cardiac injury inflicted during blood collection. I. caerulia appears to be generally more efficient than P. favidens with regard to clumping reaction. The different structural, numerical and behavioural aspects of the amoebocytes have been considered with reference to their probable causative factors and functional import.     

Basophils, IgE, and autoantibody-mediated kidney disease

Basophils are of interest in immunology due to their ability to produce a Th2-signature cytokine, IL-4, following activation. A new understanding of the role of basophils in immunity shows novel functions at a cellular level through which basophils influence adaptive immunity. This review summarizes new advances in basophil biology and discusses new roles for basophils in human disease, especially in the mediation of the pathogenesis of lupus nephritis. Recently, basophils have been shown to contribute to self-reactive Ab production in systemic lupus erythematosus and may enhance pre-existing loss of B cell tolerance, suggesting that basophils, IL-4, and IgE mediate the pathogenesis of lupus nephritis by promoting the Th2 environment and activating autoreactive B cells. In addition to envisaging exciting therapeutic prospects, these novel findings open the way for the study of basophils in other autoimmune and renal diseases.     

Expression and functions of the vascular endothelial growth factors and their receptors in human basophils

Angiogenesis is a multistep complex phenomenon critical for several inflammatory and neoplastic disorders. Basophils, normally confined to peripheral blood, can infiltrate the sites of chronic inflammation. In an attempt to obtain insights into the mechanism(s) underlying human basophil chemotaxis and its role in inflammation, we have characterized the expression and function of vascular endothelial growth factors (VEGFs) and their receptors in these cells. Basophils express mRNA for three isoforms of VEGF-A (121, 165, and 189) and two isoforms of VEGF-B (167 and 186). Peripheral blood and basophils in nasal polyps contain VEGF-A localized in secretory granules. The concentration of VEGF-A in basophils was 144.4 +/- 10.8 pg/10(6) cells. Immunologic activation of basophils induced the release of VEGF-A. VEGF-A (10-500 ng/ml) induced basophil chemotaxis. Supernatants of activated basophils induced an angiogenic response in the chick embryo chorioallantoic membrane that was inhibited by an anti-VEGF-A Ab. The tyrosine kinase VEGFR-2 (VEGFR-2/KDR) mRNA was expressed in basophils. These cells also expressed mRNA for the soluble form of VEGFR-1 and neuropilin (NRP)1 and NRP2. Flow cytometric analysis indicated that basophils express epitopes recognized by mAbs against the extracellular domains of VEGFR-2, NRP1, and NRP2. Our data suggest that basophils could play a role in angiogenesis and inflammation through the expression of several forms of VEGF and their receptors.     

Basophils in skin reactions of mast cell-deficient mice infested with Dermacentor variabilis

Acquired resistance to ticks in guinea pigs has been found to be associated with basophil-rich skin reactions. Mice, which are generally believed to possess few, if any basophils, also acquire resistance following repeated tick infestations and this has been found to be associated with increased numbers of dermal mast cells. Mast cell-deficient W/Wv mice have, however, also been shown capable of acquiring resistance after two infestations with Dermacentor variabilis larvae. In the studies described here, we have examined, with the electron microscope, skin reactions in W/Wv and +/+ mice undergoing their third infestation with Dermacentor variabilis. Basophils, along with neutrophils and eosinophils, were identified using established criteria. The possibility that basophils contribute to various pathogenetic mechanisms in these and other strains of mice is discussed.     

Differential usage of COX-1 and COX-2 in prostaglandin production by mast cells and basophils

Basophils have been erroneously considered as minor relatives of mast cells, due to some phenotypic similarity between them. While recent studies have revealed non-redundant roles for basophils in various immune responses, basophil-derived effector molecules, including lipid mediators, remain poorly characterized, compared to mast cell-derived ones. Here we analyzed and compared eicosanoids produced by mouse basophils and mast cells when stimulated with IgE plus allergens. The production of 5-LOX metabolites such as LTB4 and 5-HETE was detected as early as 0.5 h post-stimulation in both cell types, even though their amounts were much smaller in basophils than in mast cells. In contrast, basophils and mast cells showed distinct time course in the production of COX metabolites, including PGD2, PGE2 and 11-HETE. Their production by mast cells was detected at both 0.5 and 6 h post-stimulation while that by basophils was detectable only at 6 h. Of note, mast cells showed 8–9 times higher levels of COX-1 than did basophils at the resting status. In contrast to unaltered COX-1 expression with or without stimulation, COX-2 expression was up-regulated in both cell types upon activation. Importantly, when activated, basophils expressed 4–5 times higher levels of COX-2 than did mast cells. In accordance with these findings, the late-phase production of the COX metabolites by basophils was completely ablated by COX-2 inhibitor whereas the early-phase production by mast cells was blocked by COX-1 but not COX-2 inhibitor. Thus, the production of COX metabolites is differentially regulated by COX-1 and COX-2 in basophils and mast cells.     

The identification of the thyrotropic cells in the adenohypophysis of the cichlid fish Cichlasoma biocellatum and the role of these cells and of the thyroid in osmoregulation

Summary In order to identify the thyrotropic cells in the pituitary gland of Cichlasoma biocellatum, adult animals were treated with thyroxine. Periodic acid Schiff (PAS)- and aldehyde fuchsin (AF)-positive, and Alcian blue (AB)-negative basophils in the meso-adenohypophysis as well as the thyroid were strongly inactivated by such treatment. Since other cell types in the adenohypophysis were not affected, it is concluded that the PAS-positive and AB-negative basophils in the meso-adenohypophysis are the thyrotrops. In normal animals the thyrotrops and the thyroid are very active. Propylthiouracil did not cause a further activation of TSH cells. Keeping the animals in 25% sea-water caused a strong inactivation of the prolactin cells, the thyrotrops and the thyroid. In deionized water the prolactin cells were stimulated, but the thyroid was less active than in controls. Injections of ovine prolactin did not enhance the activity of the thyroid in salt water animals. It is suggested that in Cichlasoma biocellatum prolactin does not have a direct stimulatory effect on the thyroid.Thanks are due to Prof. Dr. P. G. W. J. van Oordt for his continual interest and valuable suggestions, and to Dr. L. Boomgaart for correcting the english. We are indebted also to Messrs. H. van Kooten and E. van der Vlist for making the photographs. The National Institutes of Health, Bethesda, Maryland (U.S.A.) kindly presented the ovine prolactin.     

Cytochemical observations of coelomocytes from the earthworm, Lumbricus terrestris.

Synopsis Coelomocytes of the earthworm,Lumbricus terrestris, were stained by cytochemical techniques to determine the biochemical composition of the seven different cell types and subtypes. The enzymes acid phosphatase and -glucuronidase are present in all types of coelomocytes, but are especially abundant in basophils and neutrophils; the differences in enzyme amounts correlate well with the differences in phagocytic activity of the various cell types. No peroxidase is present. The cytoplasmic basophilia of basophils is due primarily to ribonucleic acid. Basophils also contain large deposits of glycogen, with neutrophils and chloragogen cells containing somewhat lesser amounts. The predominant granules of the two types of acidophils and of granulocytes are composed of a basic protein and a neutral mucopolysaccharide or glycoprotein. A second granule population, present in low numbers in acidophils and granulocytes, but in larger numbers in basophils and neutrophils, is small in size and lipid-positive and may, in part, represent lysosomes.Lipid is especially abundant in the vesicles and granules of the two types of chloragogen cells. Some granules of chloragogen cells also contain ferrous and ferric iron and a substance with pseudoperoxidase activity. The cytoplasm contains protein, glycogen, and a neutral mucopolysaccharide. In addition, acid mucopolysaccharides are variably present in the cytoplasm of chloragogen cells, the only coelomocytes to contain this class of substances.     

HIV-1 gp120 induces IL-4 and IL-13 release from human Fc epsilon RI+ cells through interaction with the VH3 region of IgE

HIV-1 glycoprotein (gp) 120 from different clades is a potent stimulus for IL-4 and IL-13 release from basophils purified from healthy individuals seronegative for Abs to HIV-1 and HIV-2. IL-4 mRNA, constitutively present in basophils, was increased after stimulation by gp120 and was inhibited cyclosporin A and tacrolimus. IL-4 and IL-13 secretion from basophils activated by gp120 was not correlated. There was a correlation between the maximum gp120- and anti-IgE-induced IL-4 release from basophils. The average t1/2 gp120-induced IL-4 release was lower than for IL-13 release. Basophils from which IgE had been dissociated by brief exposure to lactic acid no longer released IL-4 in response to gp120 or to anti-IgE. The response to a mAb cross-linking the alpha-chain of high-affinity receptor for IgE (Fc epsilon RI) was unaffected by this treatment. Three human VH3+ monoclonal IgM inhibited gp120-induced secretion of IL-4 from basophils. In contrast, VH6+ monoclonal IgM did not inhibit the release of IL-4 induced by gp120. Synthetic peptides distant from the NH2 and COOH termini of gp120MN inhibited the activating property of gp120MN. These results indicate that gp120, which acts as a viral superantigen, interacts with the VH3 region of IgE to induce the release of IL-4 and IL-13 from human Fc epsilon RI+ cells.     

Localizing a control region in the pathway to leukotriene C(4) secretion following stimulation of human basophils with anti-IgE antibody.

Mediator release from human basophils is a self-limited process, but down-regulation of the signaling cascades leading to secretion of leukotriene C(4) (LTC(4)) is controlled independently of the pathway leading to IL-4 secretion. In the current studies, we have explored the regulation of upstream signaling events leading to activation of extracellular signal-related kinases (ERKs; previously shown to be required for LTC(4) generation) in human basophils. IgE-, but not FMLP-mediated activation, induced sustained tyrosine phosphorylation of syk, of shc, and an association of shc to the Grb2/son of sevenless 2 complex. In contrast, IgE-mediated activation resulted in transient activation of p21(ras) and mitogen-activated protein/ERK kinase 1, which were kinetically associated with phosphorylation of ERKs. The canonical Shc/Grb2/son of sevenless pathway to activation of p21(ras) is therefore sustained, while p21(ras) activity is not. We have previously shown that phosphatidylinositol 3 kinase activity is required for p21(ras) activity and, in the current studies, we show that of the p85-sensitive forms of p110 possible, basophils express only p110 delta and that there are no changes in association between p21(ras) and p110 delta in stimulated basophils. We used the generation of phospho-Akt as a marker of the presence of phosphatidylinositol-3,4,5-trisphosphate and found that phospho-Akt is transient on a time scale consistent with p21(ras) activity. On the basis of information obtained in these and other studies, we localize down-regulation of IgE-mediated LTC(4) secretion to a region of the signaling cascade antecedent to p21(ras) activation, downstream of phosphatidylinositol 3 kinase activity and probably involving regulation of phosphatidylinositol-3,4,5-trisphosphate levels.     

Selective depletion of basophils ameliorates immunoglobulin E-mediated anaphylaxis

Basophils, which are the rarest granulocytes, play crucial roles in protective immunity against parasites and development of allergic disorders. Although immunoglobulin (Ig)E-dependent responses via receptor for IgE (FcεRI) in basophils have been extensively studied, little is known about cell surface molecules that are selectively expressed on this cell subset to utilize the elimination in vivo through treatment with monoclonal antibody (mAb). Since CD200 receptor 3 (CD200R3) was exclusively expressed on basophils and mast cells (MCs) using a microarray screening, we have generated anti-CD200R3 mAb recognizing CD200R3A. In this study we examined the expression pattern of CD200R3A on leukocytes, and the influence of the elimination of basophils by anti-CD200R3A mAb on allergic responses. Flow cytometric analysis showed that CD200R3A was primarily expressed on basophils and MCs, but not on other leukocytes. Administration with anti-CD200R3A mAb led to the prominent specific depletion of tissue-resident and circulating basophils, but not MCs. Furthermore, in vivo depletion of basophils ameliorated IgE-mediated systemic and local anaphylaxis. Taken together, these findings suggest that CD200R3A is reliable cell surface marker for basophils in vivo, and targeting this unique molecule with mAb for the elimination of basophils may serve as a novel therapeutic strategy in ameliorating the allergic diseases.     

Pallial oviduct of Pomacea canaliculata (Gastropoda): ultrastructural studies of the parenchymal cellular types involved in the metabolism of perivitellins

Seasonal variations in the morphology of the parenchymal mass and function of the albumen gland/capsule gland complex have been studied in Pomacea canaliculata, together with the cellular types involved in the synthesis and secretion of perivitellin fluid components. The two major parenchymal cell types, albumen secretory cells (AS) and labyrinthic cells (LC), undergo seasonal variations throughout the annual reproductive cycle, which is divided into three periods. Both cellular types show maximal development and structural complexity during the reproductive period (spring and summer). AS cells have a well-developed Golgi complex and rough endoplasmic reticulum and their secretory granules show electron-dense particles of about 20 nm (probably galactogen). These cells are uniquely involved in ovorubin and PV2 perivitellin synthesis and their secretory granules are the single storage site for these two major perivitellins, as revealed by immunoelectron microscopy. AS also possess calcium deposits that infiltrate the cytoplasmic matrix. The luminal surfaces of LC exhibit long cilia intermingled with sparce short microvilli. Basally, the plasma membrane shows deep irregular folds that extend through the cytoplasm up to the subapical region. Calcium deposits infiltrate the cytoplasm and accumulate in the extracellular space of the basal labyrinth. Nerve terminals seem to be involved in the regulation of parenchymal cell secretion. At the post-reproductive period, AS markedly change their aspect following the release of most of the secretory granules into the acinar lumen. LC decrease in volume, the number of their cilia decreases, their cytoplasmic folds are much thinner and their extracellular spaces lack calcium particles. At the pre-reproductive period (winter), AS and LC recover and prepare for the subsequent period.This work was partially supported by grants from CIUNT, CONICET, CIC, ANPCyT and Fundación Antorchas (Argentina). R.J.P. is member of Carrera del Investigador, CIC (Bs. As.), Argentina. H.H. and M.S.D. are members of CONICET (Argentina).     

Urokinase induces basophil chemotaxis through a urokinase receptor epitope that is an endogenous ligand for formyl peptide receptor-like 1 and -like 2

Basophils circulate in the blood and are able to migrate into tissues at sites of inflammation. Urokinase plasminogen activator (uPA) binds a specific high affinity surface receptor (uPAR). The uPA-uPAR system is crucial for cell adhesion and migration, and tissue repair. We have investigated the presence and function of the uPA-uPAR system in human basophils. The expression of uPAR was found at both mRNA and protein levels. The receptor was expressed on the cell surface of basophils, in the intact and cleaved forms. Basophils did not express uPA at either the protein or mRNA level. uPA (10(-12)-10(-9) M) and its uPAR-binding N-terminal fragment (ATF) were potent chemoattractants for basophils, but did not induce histamine or cytokine release. Inactivation of uPA enzymatic activity by di-isopropyl fluorophosphate did not affect its chemotactic activity. A polyclonal Ab against uPAR inhibited uPA-dependent basophil chemotaxis. The uPAR-derived peptide 84-95 (uPAR84-95) induced basophil chemotaxis. Basophils expressed mRNA for the formyl peptide receptors formyl peptide receptor (FPR), FPR-like 1 (FPRL1), and FPRL2. The FPR antagonist cyclosporin H prevented chemotaxis induced by FMLP, but not that induced by uPA and uPAR84-95. Incubation of basophils with low and high concentrations of FMLP, which desensitize FPR and FPRL1, respectively, but not FPRL2, slightly reduced the chemotactic response to uPA and uPAR84-95. In contrast, desensitization with WKYMVm, which also binds FPRL2, markedly inhibited the response to both molecules. Thus, uPA is a potent chemoattractant for basophils that seems to act through exposure of the chemotactic uPAR epitope uPAR84-95, which is an endogenous ligand for FPRL2 and FPRL1.     

Seasonal changes in the hypothalamo-hypophyseal-ovarian system in the catfish,Heteropneustes fossilis (Bloch)*

The annual reproductive cycle of the catfish, H. fossilis (Bloch) is divided into the preparatory period (February-April), the prespawning period (May-June), the spawning period (July-August) and the postspawning period (September-January). During the early postspawning period (September-November), the hypothalamo-hypophyseal-ovarian system shows a gradual regression. In January, the hypothalamic nuclei, the pars magnocellularis (PMC), the pars parvocellularis (PPC) of the nucleus preopticus (NPO), and the nucleus lateralis tuberis (NLT) show renewed activity, as shown by a significant increase in their nuclear diameters and an accumulation of neurosecretory material (NSM) in their cell bodies. The hypophysis and the ovary remain quiescent. During the preparatory period, all the hypothalamic neurons studied indicate decreased activity but simultaneously show an accumulation of NSM in their cell bodies. The number of granulated basophils in the proximal pars distalis (PPD) of the hypophysis remains low but ovarian weights increase, presumably due to the multiplication of oogonia. In the prespawning period, there is a marked accumulation of NSM in the cell bodies of the hypothalamic neurons and at the same time the number of granulated basophils in the PPD of the hypophysis dramatically increases with concomitant increase in vitellogenic activity in the ovary. During the spawning period, the hypothalamic neurons continue to store NSM in their cell bodies and simultaneously there is a tremendous increase in the number of granulated basophils in the PPD of the hypophysis and the ovary has a large proportion of yolky primary oocytes. Spawning is associated with a significant degranulation of the granulated basophils in the PPD of the hypophysis. The significance of the results is discussed in relation to the environmental and hormonal regulation of seasonal ovarian activity.     

The thyrotropin secreting basophils in the adenohypophysis of Anoptichthys jordani

Summary In order to identify the TSH cells in the pituitary gland of Anoptichthys jordani, the development of the adenohypophysial cell types was studied in relation with the differentiation of the thyroids. In addition experiments were performed in young and adult animals with propylthiouracil (PTU) and thyroxine. At the time of the first thyroid development two meso-adenohypophysial cell types in the pituitary gland of Anoptichthys jordani are distinctly differentiated: orangeophilic cells and Alcian Blue (AB)-positive basophils. Because thyroxine and PTU could evoke changes in activity of the latter but had no effect on the orangeophils, it is concluded that the angular AB-positive basophils in the meso-adenohypophysis of Anoptichthys are responsible for the TSH production. PTU and thyroxine were unable to affect TSH cell activity in adult animals.This study was partly supported by a grant from the Netherlands Organization for the Advancement of Pure Research (Z.W.O.).I wish to thank Prof. Dr. P. G. W. J. van Oordt for his constant interest and helpful suggestions. I am indebted also to Miss M. I. Willems and Miss Tjitske van Soelen, who both gave conscientious technical assistance and to Mr. E. van der Vlist for making the photographs.     

Seasonal Changes in the Newt,Trituroides hongkongensis,Testis. I. A Histological and Histochemical Study

The testis of the newt, Trituroides hongkongensis is found to be made up of a chain of lobes each being divided into spermatogenetic zones which display seasonal cycles. Seasonal changes in the histology of the testis are studied. Lobule boundary cells are found present at the same time of the year when the secondary sex character, a lateral blue line along the tail, is best expressed. Both 5-ene-3β- and 17β-HSD activities have been located in the lobule boundary cells which are suggested to be steroidogenic and their secretion may probably be responsible for the maintenance of the secondary sex character. The Sertoli cell, which originates from the follicle cell, shows accumulation of cholesterol-positive lipid at certain stages of development but its capability in hormone production is uncertain.     

Characterization and function of the multifaceted peripheral blood basophil.

Basophils are derived from metachromatic hematopoietic precursor cells of myeloid origin. The basophilic granulocyte differentiates and matures in the bone marrow, circulates in the peripheral blood, and upon proper stimulation, migrates into the tissues. Peripheral blood basophils act as chief effector cells of the allergic response and as purveyors of various allergy-associated mediators. Under appropriate conditions, basophils can be induced to release their mediators into the extracellular space of tissues or blood of the host organism. The plasma membrane of basophils contains receptors for immunoglobulin E (IgE) homocytotropic antibody which exhibits high affinity for these granulocytes and their Fc epsilon receptors. IgE cytophilic antibody binds antigen at its Fab portion. When bound to the basophil plasma membrane, the antigen-antibody complex undergoes multivalent interactions, which create crosslinking of the Fc epsilon receptors on the basophil plasma membrane. This receptor cross-linking results in basophil degranulation and subsequent release of its pharmacologically active substances. The basophil exhibits considerable heterogeneity and is characterized as Type I, II, III, IV, V and VI based upon granule content and time of antigen stimulation. Evidence is presented showing the role of the basophil in hyperplasia, hypersensitivity, parasitic infections and other diseases.     

Environmental physiology of the teleostean thyroid gland: a review

Synopsis Recent studies of thyroid hormone function are reviewed as they relate to the environmental physiology of teleost fish. In addition, reports dealing with the apparent interdependence of thyroid gland function with that of other endocrine glands are discussed with emphasis on the interrelated endocrine response associated with changing physiological status of teleosts.Seasonal changes in thyroid gland activity are described in several species. Although seasonal alterations in apparent thyroid status are concomitant with changes in ambient temperature, photoperiod and/or gonadal status, their biological significance is not fully understood and direct relationships are for the most part, not proven. Similarly, most reports of thyroid involvement in gonadal development or maturation are based on indirect evidence of the relationship. The exception to this is a study in immature or hypophysectomized goldfish in which thyroxine (T₄) was shown to promote ovarian development and maturation, possibly acting collateralistically or synergistically with gonadotropin. Even in this study it is not clear whether the T₄ effect is a direct action on the ovarian tissue or an indirect action via the regulation of metabolites necessary for gonad metabolism. Integumentary silvering and retinal porphyropsin formation in salmonids are stimulated by administration of T₄ or thyroid extracts. Administration of T₄ or triiodothyronine (T₃) enhances skeletal and somatic growth in some teleostean species, although the effect on somatic growth is most pronounced when these hormones act synergistically with somatotropin (STH) or androgens. The growth-promoting effects of T₄ and T₃ may be linked to their apparent involvement in lipid, carbohydrate, protein and vitamin metabolism. alterations in apparent thyroid activity concomitant with changes in ambient temperature have been reported (for example correlated with seasonal ambient thermal changes), although there are marked contradictions in data presented by different investigators. Reported temperature-related effects on thyroid function are probably secondary responses of thyroid metabolism to altered temperatures. Evidence of a direct rate of thyroid hormones in the regulation of migration (and associated behavioural modifications), salmonid smoltification, oxygen consumption, and osmotic or ionic regulation although highly suggestive in a number of areas is inconclusive and requires further critical experimental evaluation.The pituitary control (by thyrotropin) of thyroid secretion of T₄ is convincingly shown in several teleosts, and evidence of an inhibitory hypothalamic control of thyrotrop activity is highly suggestive in some species. A thyrotropic effect of somatotropin preparations is well established in several teleostean species; the effect does not appear to be related to contamination of the somatotropin preparations with thyrotropin, and may be an important consideration in explaining the apparently related involvement of T₄ (or T₃) and somatotropin in growth and metabolism. The apparent thyrotropic property of some gonadotropin preparations, shown in several teleostean species, requires further investigation before the doubts regarding hormone preparation purity can be satisfied. Recent studies of effects of prolactin on thyroid function are highly suggestive of an inhibitory role of prolactin in peripheral monodeiodination of T₄ to T₃ which secondarily affects thyroid activity in some species. There is no evidence of a direct involvement of corticotropin, melanotropin or fractions of these molecules on thyroid function in teleosts. Moreover, the little evidence in support of a role of gonadal or adrenocortical steroids in thyroid control is either often contradictory or indirect and needs to be evaluated further.Interlake epizootiological studies of thyroid dysfunction in Great Lakes salmonids provide substantive evidence for the presence of a ubiquitous waterborne goitrogen(s) in the Great Lakes environs. The nature of the goitrogen(s), whether naturally-occurring or a man-introduced toxicant, remains to be determined but the possible existence of waterborne goitrogens in natural water systems and their possible effects on experimental studies of teleostean thyroid function have to be evaluated further. If goitrogens are a common component of aquatic environments their presence could explain some of the data discrepancy among different groups of investigators, and could account for some of the apparent seasonal change in teleost thyroid physiology.