Rapid induction of hypothyroidism by an avian leukosis virus

The Role of Chicken Prolactin, Growth Hormone and Their Receptors in the Immune System

Prolactin (PRL) and growth hormone (GH) exhibit important roles in the immune system maintenance. In poultry, PRL mainly plays its roles in nesting, hatching, and reproduction, while GH is primarily responding to body weight, fat formation and feed conversion. In this review, we attempt to provide a critical overview of the relationship between PRL and GH, PRLR and GHR, and the immune response of poultry. We also propose a hypothesis that PRL, GH and their receptors might be used by viruses as viral receptors. This may provide new insights into the pathogenesis of viral infection and host immune response.

Endocrine Disorders in Autoimmune Rheumatological Diseases: A Focus on Thyroid Autoimmune Diseases and on the Effects of Chronic Glucocorticoid Treatment

Autoimmune rheumatological diseases’ incidence and prevalence have risen over the last decades and they are becoming increasingly important worldwide. Thyroid autoimmune diseases share with them an imbalance in the immune system that lead to a pro-inflammatory environment. Usually this is the result of a multi-factorial process. In fact, it includes not only a possible genetic predisposition, but also environmental causes like microbiota dysbiosis, diet rich in processed foods, exposure to toxicants and infections. However, many aspects are currently under study. This paper aims to examine the factors that participate in the developing of rheumatological and thyroid autoimmune diseases. Moreover, as glucocorticoids still represent a leading treatment for systemic autoimmune rheumatological diseases, our secondary aim is to summarize the main effects of glucocorticoids treatment focusing on iatrogenic Cushing’s syndrome and glucocorticoids’ withdrawal syndrome.

A possible link between the Epstein-Barr virus infection and autoimmune thyroid disorders

The Epstein-Barr virus (EBV), also known as human herpesvirus 4, is a member of the Herpesviridae virus family. EBV infection can cause infectious mononucleosis (IM) in the lytic phase of EBV's life cycle. Past EBV infection is associated with lymphomas, and may also result in certain allergic and autoimmune diseases. Although potential mechanisms of autoimmune diseases have not been clearly elucidated, both genetic and environmental factors, such as infectious agents, are considered to be responsible for their development. In addition, EBV modifies the host immune response. The worldwide prevalence of autoimmune diseases shows how common this pathogen is. Normally, the virus stays in the body and remains dormant throughout life. However, this is not always the case, and a serious EBV-related illness may develop later in life. This explains the chronic course of autoimmune diseases that is often accompanied by exacerbations of symptoms. Based on the present studies, EBV infection can cause autoimmune diseases, such as systemic lupus erythematosus (SLE), multiple sclerosis (MS), rheumatoid arthritis (RA), Sjögren's syndrome, and autoimmune hepatitis. The EBV has also been reported in patients with autoimmune thyroid disorders. Although EBV is not the only agent responsible for the development of autoimmune thyroid diseases, it can be considered a contributory factor.

Identification of two novel multiple recombinant avian leukosis viruses in two different lines of layer chicken

Avian leukosis virus (ALV) is the most common oncogenetic retrovirus that emerges spontaneously as a result of recombination between exogenous viruses, exogenous viruses and endogenous viruses, and exogenous viruses and non-homologous cellular genes. In the present study, two natural recombinant avian leukosis viruses (rALVs) (LC110515-5 and LC110803-5) carrying a subgroup C gp85 gene, a subgroup E gp37 gene, and a subgroup J 3'UTR and 3'LTR were isolated from two different lines of layer flocks, Black-bone silky fowl (BSF) and commercial layer chicken, that suffered from myeloid leukosis. Although tumours were not observed in rALV-infected individual chickens, other non-neoplastic inflammatory lesions were evident. The two rALVs were cultured on DF-1 cells and identified by PCR, immunofluorescence assay and gene sequencing. The gp85 nucleotide sequence in the two isolates displayed a high identity (>95 %) with that of the gp85 gene in ALV-C, but the identity was less than 90 % with ALV-A/B/D/E and only 51 % with ALV-J. Phylogenetic analysis of the nucleotide and amino acid sequences confirmed that the two isolates were recombinant between ALV-C, ALV-E and ALV-J. Subgroup C ALV is rarely found in field cases. This report is the first to provide evidence that ALV-C has recombined with ALV-E and ALV-J in two different chicken lines. The source and characteristics of the two rALVs and ALV-C need to be further investigated.

Reproduction of hemangioma by infection with subgroup J avian leukosis virus: the vertical transmission is more hazardous than the horizontal way

BACKGROUND

Clinical cases of hemangioma associated with subgroup J avian leukosis virus (ALV-J) have been reported in commercial chicken layer flocks since 2006. We attempted to reproduce hemangioma through experimental infection with ALV-J to evaluate viral pathogenicity in layer birds and their progenies.

RESULTS

Body weight and indexes for immune organs of chickens infected with ALV-J strain SCDY1 were lower than those in controls. Proliferation of lymphocytes was observed in many tissues, and viral integration was detected in the genome of lymphocytes at 14 days post-infection, along with virus shedding. ALV-J was also efficiently transmitted from eggs to progenies. Embryo hatchability and progeny mortality were lower than those for controls. The efficiencies of virus shedding and virus integration in the lymphocytes of progenies were higher than those in parents.

CONCLUSIONS

ALV-J is able to inhibit the growth of infected chickens, and causes damage to immune organs. Vertical transmission of ALV-J appears to be more deleterious than horizontal transmission.

A framework for identification of infections that contribute to human obesity

WHO has declared obesity to be a global epidemic. Obesity management strategies mainly target behavioural components of the disorder, but are only marginally effective. A comprehensive understanding of the causative factors of obesity might provide more effective management approaches. Several microbes are causatively and correlatively linked with obesity in animals and human beings. If infections contribute to human obesity, then entirely different prevention and treatment strategies and public health policies could be needed to address this subtype of the disorder. Ethical reasons preclude experimental infection of human beings with candidate microbes to unequivocally determine their contribution to obesity. As an alternative, the available information about the adipogenic human adenovirus Ad36 has been used to create a template that can be used to examine comprehensively the contributions of specific candidate microbes to human obesity. Clinicians should be aware of infectobesity (obesity of infectious origin), and its potential importance in effective obesity management.

The critical time of avian leukosis virus subgroup J-mediated immunosuppression during early stage infection in specific pathogen-free chickens

The critical time of avian leukosis virus subgroup J (ALV-J)-mediated immunosuppression was determined by body weight, relative immune organ weight, histopathology, and presence of group specific antigen and antibodies in specific pathogen-free (SPF) chickens. CD4⁺ and CD8⁺ cell activity in the spleen, total and differential leukocyte counts in blood, and viral RNA levels in spleen were measured. Significant growth suppression was observed in the two ALV-J-infected groups. A strong immune response by infected groups was present in spleen at 2-weeks-of-age, but after 4-weeks-of-age, the response decreased quickly. The thymus and bursa showed persistent immunosuppression until 4-weeks-of-age. Proliferation of fibroblasts and dendritic cells were observed in immune organs at 4- and 5-weeks-of-age. However, the granulocyte cell number was markedly lower in the infected groups than in the control group. In group 1 (day 1 infection) CD4⁺ cells increased during the second week but significantly decreased during the fourth week, while group 2 (day 7 infection) showed the opposite effect. Viral RNA increased significantly by the fourth week. These data identify 3~4 weeks post-infection as the key time at which the ALV-J virus exerts its immunosuppressive effects on the host.

Unconventional wisdom about the obesity epidemic

Diet and sedentary lifestyle, interacting with "thrifty" genes, are widely accepted as the principal cause of the current global obesity epidemic. However, a number of alternative etiologies for obesity have been proposed, including "drifty" genes, viruses, bacteria, environmental toxins, social network effects, maternal imprinting, sleep deprivation, and others. These Grand Rounds reviews the background of some of these unconventional ideas and evidence for or against their roles in the obesity epidemic.

Viral obesity: fact or fiction?

The aetiology of obesity is multifactorial. An understanding of the contributions of various causal factors is essential for the proper management of obesity. Although it is primarily thought of as a condition brought on by lifestyle choices, recent evidence shows there is a link between obesity and viral infections. Numerous animal models have documented an increased body weight and a number of physiologic changes, including increased insulin sensitivity, increased glucose uptake and decreased leptin secretion that contribute to an increase in body fat in adenovirus-36 infection. Other viral agents associated with increasing obesity in animals included canine distemper virus, rous-associated virus 7, scrapie, Borna disease virus, SMAM-1 and other adenoviruses. This review attempted to determine if viral infection is a possible cause of obesity. Also, this paper discussed mechanisms by which viruses might produce obesity. Based on the evidence presented in this paper, it can be concluded that a link between obesity and viral infections cannot be ruled out. Further epidemiologic studies are needed to establish a causal link between the two, and determine if these results can be used in future management and prevention of obesity.

Infeccions as the etiology for obesity

The role of infection on obesity development has been questioned since the early 1980's. Several studies on animals have shown that fisiopathologic mechanisms through which infections can produce obesity do exist. At least eight types of obesity-inducing viruses have been identified in animals, especially poultry and mice. Studies on humans are far less convincing; however, two adenoviruses, Ad-36 and SMAM-1, have shown adipogenic properties. In vitro studies with 3T3-L1 cells stated the activation of the enzymatic pathway that leads to fatty tissue accumulation; in vivo studies have also detected higher levels of antibodies against such viruses on obese subjects. Although most known infections nowadays cause obesity through central nervous system lesions, the Ad-36 adenovirus infection affects fatty tissue directly, raising doubts regarding central role component in this case.

Suppression of iodide uptake and thyroid hormone synthesis with stimulation of the type I interferon system by double-stranded ribonucleic acid in cultured human thyroid follicles

Although viral infection is thought to be associated with subacute thyroiditis and probably with autoimmune thyroid disease, possible changes in thyroid function during the prodromal period of infection or subclinical infection remain largely unknown. Recently, it was shown that pathogen-associated molecular patterns stimulate Toll-like receptors (TLR) and activate innate immune responses by producing type I interferons (IFN). Using a human thyroid follicle culture system, in which de novo synthesized thyroid hormones are released into the culture medium under physiological concentrations of human TSH, we studied the effects of polyinosinic-polycytidylic acid [Poly(I:C)], a chemical analog of viral double-stranded RNA (dsRNA), on TSH-induced thyroid function. Thyrocytes expressed ligands for dsRNA (TLR 3, CD14, and retinoic-acid-inducible protein-1) comparable with the TSH receptor. DNA microarray and real-time PCR analyses revealed that dsRNA increased the expression of mRNA for TLR3, IFN-beta, IFN-regulating factors, proinflammatory cytokines, and class I major histocompatibility complex (MHC), whereas genes associated with thyroid hormonogenesis (sodium/iodide symporter, peroxidase, deiodinases) were suppressed. In accordance to these data, Poly(I:C) suppressed TSH-induced 125I uptake and hormone synthesis dose dependently, accompanied by a decrease in the ratio of 125I-T3/125I-T4 released into the culture medium, whereas peptidoglycan, lipopolysaccharides, or unmethylated CpG DNA, ligands for TLR2, TLR4, and TLR9, respectively, had no significant effect. These inhibitory effects of Poly(I:C) were not blocked by a neutralizing antibody against TLR3 and an anti-IFN alpha/beta receptor antibody. These in vitro findings suggest that when thyrocytes are infected with certain viruses, dsRNA formed intracellularly in thyrocytes may be a cause for thyroid dysfunction, leading to development of autoimmune thyroiditis.

Differences in pathogenicity among strains of the same or different avian leukosis virus subgroups

An efficient induction of wasting disease in chickens by avian leukosis virus (ALV), particularly ALV subgroup C, requires >102 infectious units virus inoculated in mid embryogenesis. The most conspicuous symptoms of the disease were induced by ALV subgroup C; however, significant differences in the occurrence of wasting disease were found among individual members of this subgroup. Almost comparable pathogenicity was exhibited by ALV subgroup D, whereas viruses of subgroups B and A proved to be moderately and almost non-pathogenic, respectively. Using antibodies to cellular antigens, tissue alterations were shown clearly in ALV-C-infected chickens. An essential feature was depletion of lymphocytes in the thymus, bursa and spleen. While the number of dendritic cells in the bursa was increased, their representation in the thymus and spleen was reduced. In the spleen, however, the reduction of dendritic cells concerned only an ellipsoid compartment, which in itself was also markedly reduced. An increased number of macrophages in the thymus and spleen corresponded with the observed general activation of the monocyte-macrophage system. In the spleen, CD4+ T cells were reduced while CD8+ T cells were increased. In agreement with this finding was a failure of chickens to respond to Brucella antigen and an inability of their splenocytes to respond to Concanavalin A, both of which pointed to the damage of immune reactivity. Variation in the pathogenicity among individual ALV strains provides ground for depicting gene sequences playing an important role in ALV acute pathogenicity.

Could a virus contribute to weight gain?

OBJECTIVE

Obesity is a serious public health problem associated with increased morbidity and mortality. Although the causes for obesity are unclear, it seems that environmental, genetic, neural and endocrine factors contribute to its development. However, the rapid global spread of obesity resembles epidemiologically the spread of an infectious disease. Thus far, little consideration has been given to the possibility that the epidemic of obesity could be due to an infectious agent. Seven viruses and a scrapie agent have been implicated in obesity.

DESIGN

This review evaluates the infectious pathogens and the evidence that these viruses are associated with obesity and concludes that a strong evidence base is emerging that associates certain viruses with obesity.

CONCLUSION

More work is however required to elucidate the mechanisms of weight gain after viral infection. In the mean time, discounting viruses as a contributing factor to obesity would deprive us of a potential new avenue of investigating and treating the ever increasing epidemic of obesity.

Infectobesity: Obesity of Infectious Origin

The rapid increase in obesity and the associated health care costs have prompted a search for better approaches for its prevention and management. Such efforts may be facilitated by better understanding the etiology of obesity. Of the several etiological factors, infection, an unusual causative factor, has recently started receiving greater attention. In the last two decades, 10 adipogenic pathogens were reported, including human and nonhuman viruses, scrapie agents, bacteria, and gut microflora. Some of these pathogens are associated with human obesity, but their causative role in human obesity has not been established. This chapter presents information about the natural hosts, signs and symptoms, and pathogenesis of the adipogenic microorganisms. If relevant to humans, "Infectobesity" would be a relatively novel, yet extremely significant concept. A new perspective about the infectious etiology of obesity may stimulate additional research to assess the contribution of hitherto unknown pathogens to human obesity and possibly to prevent or treat obesity of infectious origins.

Myotropic avian leukosis virus subgroup J infection in a chicken

The study describes a highly productive myotropic avian leukosis virus infection (ALV) in a 3-month-old female chicken. At necropsy, ascites, hepatic fibrosis and cardiomegaly were seen. Histologically, the most striking lesion was the presence of cytoplasmic basophilic inclusions in myocardial fibers. Immunostaining for ALV group specific antigen p27 revealed a diffuse presence of virus antigen in cardiac myofibers, in smooth muscle fibers of most of the organs, and in rare, pancreatic and ovarian theca cells. Ultrastructurally, myocardial inclusions consisted of clusters of 50-60 nm round particles with interspersed ribosome-like granules. Numerous C-type particles were found in intercellular spaces of ALV p27 positive tissues. PCR analyses revealed the presence of both ALV-E and ALV-J related sequences. In chicken genome, ALV-E is usually present as endogenous provirus therefore, the pathological findings observed in this case are considered to be related with the ALV-J infection. The results of this report further confirm that ALV-J may be responsible for highly productive myotropic infections.

Self-recognition and the role of fetal microchimerism

The course and severity of the autoimmune thyroid diseases (AITD) is known to be influenced by pregnancy as evidenced by disease suppression during pregnancy and initiation, or exacerbation, of disease postpartum. AITD is also known to affect both fertility and pregnancy outcome as evidenced by increased fetal loss. However, the precise mechanisms of this influence have not been fully understood. Here we have reviewed the mechanisms of self-recognition thought to be active in AITD and we have included recent information on the potential role of fetal microchimerism (exposure of paternal antigen to the mother during and after pregnancy).

Effect of an in ovo infection with a Dutch avian leukosis virus subgroup J isolate on the growth and immunological performance of SPF broiler chickens

The effect of an in ovo infection with a Dutch isolate of avian leukosis virus subgroup J (ALV-J) on the growth of specific pathogen free (SPF) broiler chickens was analysed. During this study, possible immune suppressive effects of ALV-J were assessed by measuring delayed-type hypersensitivity with keyhole limpet haemocyanin (KLH), natural killer (NK) cell activity, the production of radicals of nitric oxide (NO) by macrophages, humoral immune response against Newcastle and infectious bursal disease vaccine viruses, and automated total and differential leukocyte counts. In an attempt to elucidate the underlying causal mechanisms of the induced growth retardation, 3,3',5-triiodothyronine (T3) concentrations in serum were measured. Four experiments were conducted. In experiment 1, ALV-J-injected birds were compared with ALV subgroup A (ALV-A)-injected and negative control chickens. In experiment 2, ALV-J-injected birds were only compared with negative controls. Finally, in experiments 3a and 3b, ALV-J-injected chickens were compared with negative controls and a group of chickens in which only 10% of birds had been injected with ALV-J. Birds were injected in ovo at day 7 of incubation with 10(4) median tissue culture infectious dose (TCID(50)) ALV-J or ALV-A, except in experiment 3a where 10(2) TCID(50) ALV-J was injected. Significant growth suppression was found in all 100% of ALV-J-infected groups. The average growth retardation of ALV-J-infected birds compared with negative controls at 6 weeks of age was approximately 8, 11, 2.5 and 6% for the four successive experiments performed. The delayed-type hypersensitivity test against KLH of ALV-J-infected birds showed a tendency towards lower wattle thickness; however, the difference with controls was not significant (P > 0.05). The same was true for NK cell activity and NO production by macrophages, although the difference was not significant. The total and differential leukocyte counts performed on blood samples from birds at 3, 4 and 6 weeks of age as well as the humoral immune response against Newcastle and infectious bursal disease vaccine viruses did not show significant differences between treatment groups either. Only the number of basophils were significantly higher (P = 0.02) in ALV-J-infected birds at 3 weeks of age. No significant lower T(3) levels were found in ALV-J-infected birds in weeks 2 and 3 (experiment 2) and weeks 3 and 5 (experiment 3b); however, at 4 weeks (experiment 2) and 6 weeks (experiment 3b) of age, T(3) levels were significantly lower suggesting mild hypothyroidism in these broilers. In conclusion, the present experiments show the occurrence of significant growth retardation in SPF broilers after an ALV-J in ovo infection. The various studies performed to assess the immune competence of ALV-J-infected chickens did not show significant differences in immune responsiveness. The assays on cellular immunity showed a tendency to a lower response in ALV-J-infected birds, but these differences were not statistically significant.

Localization of avian leukosis virus subgroup J in naturally infected chickens by RNA in situ hybridization

The novel subgroup J of avian leukosis virus (ALV-J) has emerged as a significant cause of myeloid neoplasia and weight suppression in broiler chickens. We investigated viral tropism using RNA in situ hybridization (ISH) in naturally infected chickens. Formalin-fixed tissues were collected from 12-day-old embryos (seven infected, two control) and from 0-week-old (four infected, one control), 3-week-old (five infected, one control), 6-week-old (five infected, one control), and 9-week-old (10 infected, two control) chickens naturally infected with ALV-J in ovo. A 636-base antisense riboprobe complementary to the 3' and 5' ends of the pol and env viral genes, respectively, was constructed. Strong positive staining was present in cardiac myocytes, Purkinje fibers, vascular and pulmonary smooth muscle, renal glomeruli, distal tubules, and pituitary glands. Light staining was present in gastrointestinal smooth muscle, thyroid and adrenal glands, and follicular medullae in the cloacal bursa. Staining was not present in any hematopoietic precursors. Tissues from newly hatched chicks exhibited the strongest and most consistent staining, whereas staining in embryos was minimal. RNA ISH confirmed the presence of ALV-J-specific nucleic acid within cytoplasmic inclusions in cardiac myocytes, Purkinje fibers, pituitary glands, and renal glomeruli. Viral tropism for cardiac myocytes and Purkinje fibers may relate pathogenetically to the cardiomyopathy and congestive heart failure described in index chicken flocks infected with ALV-J. Viral tropism for endocrine organs may relate pathogenetically to the weight suppression associated with infection.

Involvement of Epitope Mimicry in Potentiation But Not Initiation of Autoimmune Disease

We have examined whether the peptide (368–381) from the murine adenovirus type 1 E1B sequence, exhibiting a high degree of homology with the known pathogenic thyroglobulin (Tg) T cell epitope (2695–2706), can induce experimental autoimmune thyroiditis (EAT) in SJL/J mice. The viral peptide was a poor immunogen at the T or B cell level and did not elicit EAT either directly or by adoptive transfer assays. Surprisingly, however, the viral peptide was highly antigenic in vitro, activating a Tg2695–2706-specific T cell clone and reacting with serum IgG from mice primed with the Tg homologue. The viral peptide also induced strong recall responses in Tg2695–2706-primed lymph node cells, and subsequent adoptive transfer of these cells into naive mice led to development of highly significant EAT. These data demonstrate that nonimmunogenic viral peptides can act as agonists for preactivated autoreactive T cells and suggest that epitope mimicry may at times play a potentiating rather than a precipitating role in the pathogenesis of autoimmune disease.

Lymphoid leukosis viruses, their recognition as 'persistent' viruses and comparisons with certain other retroviruses of veterinary importance

Diseases caused by lymphoid leukosis virus (LLV), a retrovirus, take a long time after infection to develop and have a wide variety of pathological manifestations. This long latent period is characteristic of 'persistent virus infections'. Disease produced by LLV infection and its underlying mechanisms is compared with 'persistent' infections caused by other retroviruses in birds and mammals of veterinary importance. The diseases considered for comparison are those caused by reticuloendotheliosis, feline leukaemia, bovine leukosis and equine infectious anaemia viruses. There are significant changes in the immunological status in all diseases caused by these viruses. LLV infections follow this trend with, in manifestations of neoplastic disease, a perturbation of the normal switch that occurs from IgM to IgG synthesis. There are also indications of other immunological disturbances. Factors other than immunological disturbances may contribute to the length of time after infection required for the many forms of LLV infection to appear. Such additional factors may include the operation of 'biological clocks', such as the arrival of sexual maturity, and also the very nature of retroviruses. These factors, like the immunological changes, play major roles in the maintenance and progression of persistent retrovirus infections.

Infections and autoimmune endocrine disease

The literature examined in this review points to the possible involvement of infectious agents in the pathogenesis of autoimmune endocrine diseases, primarily autoimmune thyroid disease and diabetes mellitus. Various mechanisms have been proposed to explain induction of autoimmunity by infection but it seems that three possibilities may be important in individuals susceptible to developing autoimmune disease: molecular mimicry (perhaps to retroviruses); polyclonal T cell activation (by an endogenous superantigen or an infecting organism); and MHC class II antigen induction. It seems reasonable that all three mechanisms operate together or separately in different individuals. Data continue to accumulate in favour of infectious agents being important initiators of autoimmune disease.

Reflections on the pathogenesis of diseases caused by the acute avian leukosis/sarcoma viruses with special reference to avian erythroblastosis

The various diseases that follow experimental infection with the acute and non-acute avian oncoviruses are discussed with special reference to the pathogenesis of avian erythroblastosis. One view, based on in vitro studies, sees erythroblastosis as the product of a failure in the differentiation of virus-infected stem cells to mature erythrocytes, as a result of cell 'transformation'. The results of some in vivo studies, however, point to a resemblance of the disease to a haemolytic anaemia, where cellular death is an important component. It seems probable that the disease is the result of transformation of cells of the erythroblastic series followed by the death of many of these cells due to influences that have not yet been determined. Determination of the causes of this cellular death may prove to be as important for our understanding of the problem of leukaemia as the work that has already been accomplished in explaining the causes of cell transformation. It is also suggested that the tendency of gs amino acid sequences of the avian leukosis viruses and mouse leukaemia viruses to form fusion proteins with a variety of proto-oncogenes may be part of a wider phenomenon, and that these sequences may fuse with other proteins, altering their properties. More work is required on the possibility that there is an undiscovered immunological component in the progression of the L/S diseases.

Functional and structural alterations of the nervous system induced by avian retrovirus RAV-7

Chickens infected as embryos with RAV-7 developed neurological signs including ataxia, lethargy, and imbalance. Evoked spinal cord potentials for RAV-7 infected SC chickens were considerably slower (64.8 m/s) than for uninfected SC (103.4 m/s), genetically hypothyroid (OS) (93.9 m/s) or special C (95.1 m/s) chickens. Conduction velocity measurements of sciatic nerves showed normal values for all the chickens examined in this study. Histopathological studies revealed non-suppurative meningoencephalomyelitis in RAV-7 infected SC chickens. The inflammatory infiltrate consisted of lymphocytes, macrophages, and occasional plasma cells. The cells in the infiltrate reacted with mouse monoclonal antibodies directed against la and T-cell antigens. Astrocytic hypertrophy and hyperplasia, demonstrated by the use of monoclonal antibody specific for glial fibrillary acidic protein (GFAP), was associated with the CNS lesions. The results of this investigation indicate that RAV-7 causes significant central nervous system lesions and functional impairment in the infected chicken. This system may serve as a useful model for studying retrovirus-induced neurological dysfunction.

Effect of Rous associated virus number 7 on lymphoid cells and tissues of the chicken

Infection of chicks or chick embryos with Rous associated virus number 7 (RAV-7) led to a decreased blastogenic response to Concanavalin A (Con A) by lymphocytes isolated from the spleen and thymus. Chicks infected with RAV-7 8 days after hatch manifested decreased Con A blastogenesis 5 weeks postinfection, while chicks infected in ovo at 10 days of incubation showed an unusual pattern of cell density dependent decreased blastogenesis two weeks post-hatch (three weeks post-infection). Histopathological examination of tissues from RAV-7 infected chicks revealed evidence of lymphoid organ involution and widespread lymphoproliferative lesions by 3 weeks of age. The combination of decreased in vitro lymphoid blastogenesis and in vivo lymphoproliferation suggests that RAV-7 interacts with lymphocytes in a fashion that has not previously been described in the chicken.

Specificity of avian leukosis virus-induced hyperlipidemia

Rous-associated virus 7 (RAV-7) is a subgroup C avian leukosis virus which does not transform cells in vitro or carry an oncogene. When injected into 1-day-old hatched chicks, RAV-7 causes a low incidence of lymphoid leukosis after a latent period of several months. In contrast, infection of 10-day-old chicken embryos with RAV-7 leads to a disease syndrome characterized by stunting, obesity, atrophy of the bursa and the thymus, high triglyceride and cholesterol levels, reduced thyroxine levels, and increased insulin levels (Carter et al., Infect. Immun. 39:410-422, 1983; J.K. Carter and R.E. Smith, Infect. Immun. 40:795-805, 1983). Histopathological examination of tissues from affected chicks revealed an accumulation of lipid in the liver and an extensive infiltration of the thyroid and pancreas by lymphoblastoid cells. In the present investigation, the subgroup specificity of this syndrome was investigated. Other subgroup C avian leukosis viruses (transformation-defective B77, transformation-defective Prague C strain of Rous sarcoma virus, and RAV-49) caused stunting, infiltration of the thyroid and pancreas, increased liver weights, decreased thyroxine levels, and increased insulin levels, but they did not cause a uniform, profound increase in triglyceride and cholesterol levels. Avian leukosis viruses of subgroup A [myeloblastosis-associated virus 1 causing osteopetrosis [MAV-1(O)] and RAV-1], subgroup B [MAV-2(O), MAV-2 causing nephroblastoma [MAV-2(N)], and RAV-2], subgroup D (RAV-50), and subgroup F (ring-necked pheasant virus and RAV-61) did not cause a syndrome identical to that induced by RAV-7. All of the viruses examined induced some stunting and a reduction in thyroxine levels which correlated with the stunting. The two subgroup F viruses caused an infiltration of the thyroid which may have been secondary to severe lung involvement. We conclude that the RAV-7 syndrome is unique, particularly in the induction of a hyperlipidemia.