Charakterisierung des Zytokins BAFF als wichtiger Regulator der B-Zellfunktion beim Haushuhn

This investigation is based on the identification of cDNA sequence information for a putative chicken homologue of the mammalian cytokine “B cell activating factor belonging to the TNF family” (BAFF) in a chicken EST-database. The cDNAs encoded for the complete open reading frame of chicken BAFF (chBAFF) including a transmembrane domain and a potential furine cleavage side. ChBAFF shows an uncommon high amino-acid sequence identity with 76% identity to human BAFF in comparison with other chicken cytokines. To investigate its biochemical and functional properties, recombinant prokaryotic chBAFF was generated in E. coli and eukaryotic chBAFF was obtained from transfected 293T cells. A polyclonal rabbit antiserum raised against His-chBAFF reacted with both, the prokaryotic and the eukaryotic cytokine and was used to quantify 293T cell derived chBAFF in an ELISA system. Studies by northern blot analysis revealed a strong expression signal in the Bursa of Fabricius and a weak signal in the spleen, while all other tissues including thymus and gut tissue were negative. In situ hybridisation detected a wide distribution pattern for chBAFF-mRNA in all areas of the bursa of Fabricius. However, the strongest expression was seen in the medulla from bursal follikels. These studies indicate that both the bursal stroma and bursal B-cells must be considered as potential sources for chBAFF. To identify target cells for this cytokine, chBAFF receptor(s) expression was investigated in binding studies with Flag tagged chBAFF (Flag-chBAFF) and binding was analysed by flow cytometry. Receptor expression was clearly restricted to B-cells including mature B-cells from peripheral lymphoid organs as well as immature bursal B-cells. Subsequent studies on the ontogeny of chBAFF receptor expression showed a positive correlation between the cytokine receptor expression and the expression of the B-cell antigen receptor in the developing embryonic bursa. Receptor-ligand-interaction ELISA and co-immunoprecipitation experiments demonstrated that chBAFF binds to all three mammalian BAFF receptors identified thus far. Importantly, studies of chBAFF binding to the chicken B-cell line DT40 showed that an engineered soluble form of the human BAFF-receptor BCMA (huBCMA-Fc) inhibited chBAFF binding. The addition of 293T cell derived chBAFF to splenic lymphocyte cultures led to a significant increase in B-cell viability. This dose-dependent effect was also observed in lymphocyte cultures from ceacal tonsils and in cultures of purified (>95%) splenic B-cell preparations. While the rapid apoptosis in cultures of bursal lymphocytes could not be completely prevented, chBAFF clearly increased the survival of these immature B-cells. CFSE labelling experiments further showed that chBAFF did not induce B-cell proliferation. Therefore, it is highly probable that chBAFF, as its mammalian counterpart, is a potent inhibitor of B-cell apoptosis. These in vitro studies were complemented by in vivo experiments with purified prokaryotic chBAFF. Daily injection of recombinant cytokine for 7 days induced a significant increase in spleen weight and B-cell frequency in spleen and caecal tonsils. Besides, the functional overexpression of chBAFF induced significantly (4-fold) increased serum IgM levels. Therefore, chBAFF does not only increase B cell numbers, it also influences their differentiation to antibody secreting cells. However, no effect was observed on the bursa of Fabricius prompting the reverse experimental approach. With the availability of a soluble cytokine specific receptor (huBCMA-Fc) in vivo knockdown studies could be performed. Daily i.p. application of huBCMA-Fc to newly hatched birds for 5 days led to decreased spleen weights and drastically reduced the B-cell frequency in spleens and caecal tonsils. In addition, bursal weights in treated birds were lower than in untreated controls. This experiment in combination with the observation of high expression levels of chBAFF-mRNA in the bursa and functional BAFF-receptor(s) on bursal B-cells strongly indicated a thus far unknown role for BAFF in early B-cell development.Die Grundlage der vorliegenden Arbeit bildete die Identifizierung der cDNA-Sequenz eines aviären Homologes zum „B cell activating factor belonging to the TNF family“ (BAFF) des Säugers in einer Hühner EST-Datenbank. Diese cDNA-Sequenz kodiert für den kompletten offenen Leserahmen von chBAFF und enthält neben einer Transmembrandomäne auch eine mögliche Furin-Schnittstelle. Mit einer Aminosäuren-Identität von 76% zwischen chBAFF und dem humanen BAFF weist es eine bedeutend höhere Homologie auf als andere bekannte Hühner-Zytokine. Zur biochemischen und funktionellen Charakterisierung des Zytokins wurde dieses in rekombinanter Form sowohl prokaryotisch in E.coli als auch eukaryotisch in 293T Zellen exprimiert. Das prokaryotisch exprimierte His-chBAFF wurde zur Gewinnung eines polyklonalen Kaninchen-Antiserums verwendet. Die daraus gereinigte IgG-Fraktion ermöglicht den Nachweis von pro- und eukaryotisch exprimiertem Zytokin und wurde zur Quantifizierung von chBAFF im ELISA herangezogen. Northern Blot Studien zeigten eine schwache chBAFF-Expression in der Milz und ein starkes Expressionssignal in der Bursa Fabricii, während alle weiteren getesteten Gewebe, wie Thymus und Darm, negativ waren. In der in situ Hybridisierung wies die mRNA für chBAFF ein breites Verteilungsmuster über das gesamte Organ auf, wobei in der Follikelmedulla eine verstärkte Expression detektiert werden konnte. Aufgrund der vorliegenden Daten sind daher als Quelle für das Zytokin sowohl bursale B-Zellen als auch Stromazellen in Betracht zu ziehen. Zur Identifikation der Zielzellen des Zytokins wurde die Expression der chBAFF-Rezeptor(en) in durchflusszytometrischen Bindungsstudien mit Flag-chBAFF analysiert. Hierbei konnten Rezeptoren für chBAFF ausschließlich auf B-Zellen nachgewiesen werden und zwar sowohl auf reifen B-Zellen aus peripheren lymphatischen Organen als auch auf den unreifen B-Zellen der Bursa. Nachfolgende Studien zur Rezeptorontogenese ergaben eine deutliche positive Korrelation zwischen der Expression des Zytokinrezeptors und derjenigen des B-Zellrezeptors in der embryonalen Bursa. Im Rezeptor-Ligand-Interaktions-ELISA konnte ebenso wie durch Ko-Immuno-präzipitation eine Bindung von chBAFF an alle drei bislang bekannten BAFF-Rezeptoren des Säugers gezeigt werden. Von besonderer Bedeutung war hierbei, dass die chBAFF-Bindung an die Hühner-B-Zelllinie DT40 durch eine lösliche Variante des humanen BAFF-Rezeptors BCMA (huBCMA-Fc) blockiert werden konnte. Der Zusatz von eukaryotisch exprimiertem chBAFF zu Kulturen aus Milzlymphozyten führte zu einem signifikanten Anstieg der Zahl lebender B-Zellen. Dieser dosisabhängige Effekt war auch in Lymphozytenkulturen aus Caecaltonsillen und in Kulturen gereinigter (>95%) B-Zellpräparationen aus der Milz zu beobachten. Die rasche Apoptose bursaler Lymphozyten in Kultur konnte zwar nicht gänzlich verhindert werden, die Supplementierung von chBAFF führte aber auch in Kulturen dieser unreifen B-Zellen zu einer deutlichen Zunahme der Viabilität. Anschließende Experimente mit CFSE markierten Zellen ergaben, dass chBAFF nicht zur Proliferation der B-Zellen führt. Die nachgewiesenen Effekte werden folglich mit großer Wahrscheinlichkeit durch die potente Inhibition der Apoptose der B-Zellen verursacht. Die Zellkulturarbeiten konnten durch in vivo Studien mit gereinigtem prokaryotischem chBAFF bestätigt werden. Die tägliche Injektion des rekombinanten Zytokins über sieben Tage hinweg induzierte dabei eine signifikante Zunahme von Milzgewicht und B-Zellfrequenz in Milz und Caecaltonsillen. Zusätzlich kam es durch die funktionelle chBAFF-Überexpression zu einem signifikanten (4-fachen) Anstieg der IgM-Serumspiegel. Somit scheint chBAFF nicht nur die Zahl der B-Zellen zu beeinflussen, sondern auch deren Differenzierung zu Antikörper sekretierenden Zellen. Da durch die Supplementierung des Zytokins keine Effekte auf die Bursa erzielt werden konnten, wurde nachfolgend der umgekehrte experimentelle Ansatz gewählt und endogenes chBAFF bei frisch geschlüpften Küken fünf Tage lang durch die tägliche i.p. Injektion von huBCMA-Fc neutralisiert. Dieser funktionelle Knockdown führte zur Abnahme des Milzgewichts und einer drastischen Reduktion der B-Zellfrequenz in Milz und Caecaltonsillen. Zudem konnte eine Verringerung der Bursagewichte beobachtet werden. Dieser Befund, sowie die vorrangige chBAFF-mRNA-Expression in der Bursa und die Expression seiner Rezeptoren auf bursalen B-Zellen, deuten zusammengenommen auf eine bislang unbekannte Rolle von BAFF in der frühen B-Zellentwicklung hin

Charakterisierung des Zytokins BAFF als wichtiger Regulator der B-Zellfunktion beim Haushuhn

This investigation is based on the identification of cDNA sequence information for a putative chicken homologue of the mammalian cytokine “B cell activating factor belonging to the TNF family” (BAFF) in a chicken EST-database. The cDNAs encoded for the complete open reading frame of chicken BAFF (chBAFF) including a transmembrane domain and a potential furine cleavage side. ChBAFF shows an uncommon high amino-acid sequence identity with 76% identity to human BAFF in comparison with other chicken cytokines. To investigate its biochemical and functional properties, recombinant prokaryotic chBAFF was generated in E. coli and eukaryotic chBAFF was obtained from transfected 293T cells. A polyclonal rabbit antiserum raised against His-chBAFF reacted with both, the prokaryotic and the eukaryotic cytokine and was used to quantify 293T cell derived chBAFF in an ELISA system. Studies by northern blot analysis revealed a strong expression signal in the Bursa of Fabricius and a weak signal in the spleen, while all other tissues including thymus and gut tissue were negative. In situ hybridisation detected a wide distribution pattern for chBAFF-mRNA in all areas of the bursa of Fabricius. However, the strongest expression was seen in the medulla from bursal follikels. These studies indicate that both the bursal stroma and bursal B-cells must be considered as potential sources for chBAFF. To identify target cells for this cytokine, chBAFF receptor(s) expression was investigated in binding studies with Flag tagged chBAFF (Flag-chBAFF) and binding was analysed by flow cytometry. Receptor expression was clearly restricted to B-cells including mature B-cells from peripheral lymphoid organs as well as immature bursal B-cells. Subsequent studies on the ontogeny of chBAFF receptor expression showed a positive correlation between the cytokine receptor expression and the expression of the B-cell antigen receptor in the developing embryonic bursa. Receptor-ligand-interaction ELISA and co-immunoprecipitation experiments demonstrated that chBAFF binds to all three mammalian BAFF receptors identified thus far. Importantly, studies of chBAFF binding to the chicken B-cell line DT40 showed that an engineered soluble form of the human BAFF-receptor BCMA (huBCMA-Fc) inhibited chBAFF binding. The addition of 293T cell derived chBAFF to splenic lymphocyte cultures led to a significant increase in B-cell viability. This dose-dependent effect was also observed in lymphocyte cultures from ceacal tonsils and in cultures of purified (>95%) splenic B-cell preparations. While the rapid apoptosis in cultures of bursal lymphocytes could not be completely prevented, chBAFF clearly increased the survival of these immature B-cells. CFSE labelling experiments further showed that chBAFF did not induce B-cell proliferation. Therefore, it is highly probable that chBAFF, as its mammalian counterpart, is a potent inhibitor of B-cell apoptosis. These in vitro studies were complemented by in vivo experiments with purified prokaryotic chBAFF. Daily injection of recombinant cytokine for 7 days induced a significant increase in spleen weight and B-cell frequency in spleen and caecal tonsils. Besides, the functional overexpression of chBAFF induced significantly (4-fold) increased serum IgM levels. Therefore, chBAFF does not only increase B cell numbers, it also influences their differentiation to antibody secreting cells. However, no effect was observed on the bursa of Fabricius prompting the reverse experimental approach. With the availability of a soluble cytokine specific receptor (huBCMA-Fc) in vivo knockdown studies could be performed. Daily i.p. application of huBCMA-Fc to newly hatched birds for 5 days led to decreased spleen weights and drastically reduced the B-cell frequency in spleens and caecal tonsils. In addition, bursal weights in treated birds were lower than in untreated controls. This experiment in combination with the observation of high expression levels of chBAFF-mRNA in the bursa and functional BAFF-receptor(s) on bursal B-cells strongly indicated a thus far unknown role for BAFF in early B-cell development.Die Grundlage der vorliegenden Arbeit bildete die Identifizierung der cDNA-Sequenz eines aviären Homologes zum „B cell activating factor belonging to the TNF family“ (BAFF) des Säugers in einer Hühner EST-Datenbank. Diese cDNA-Sequenz kodiert für den kompletten offenen Leserahmen von chBAFF und enthält neben einer Transmembrandomäne auch eine mögliche Furin-Schnittstelle. Mit einer Aminosäuren-Identität von 76% zwischen chBAFF und dem humanen BAFF weist es eine bedeutend höhere Homologie auf als andere bekannte Hühner-Zytokine. Zur biochemischen und funktionellen Charakterisierung des Zytokins wurde dieses in rekombinanter Form sowohl prokaryotisch in E.coli als auch eukaryotisch in 293T Zellen exprimiert. Das prokaryotisch exprimierte His-chBAFF wurde zur Gewinnung eines polyklonalen Kaninchen-Antiserums verwendet. Die daraus gereinigte IgG-Fraktion ermöglicht den Nachweis von pro- und eukaryotisch exprimiertem Zytokin und wurde zur Quantifizierung von chBAFF im ELISA herangezogen. Northern Blot Studien zeigten eine schwache chBAFF-Expression in der Milz und ein starkes Expressionssignal in der Bursa Fabricii, während alle weiteren getesteten Gewebe, wie Thymus und Darm, negativ waren. In der in situ Hybridisierung wies die mRNA für chBAFF ein breites Verteilungsmuster über das gesamte Organ auf, wobei in der Follikelmedulla eine verstärkte Expression detektiert werden konnte. Aufgrund der vorliegenden Daten sind daher als Quelle für das Zytokin sowohl bursale B-Zellen als auch Stromazellen in Betracht zu ziehen. Zur Identifikation der Zielzellen des Zytokins wurde die Expression der chBAFF-Rezeptor(en) in durchflusszytometrischen Bindungsstudien mit Flag-chBAFF analysiert. Hierbei konnten Rezeptoren für chBAFF ausschließlich auf B-Zellen nachgewiesen werden und zwar sowohl auf reifen B-Zellen aus peripheren lymphatischen Organen als auch auf den unreifen B-Zellen der Bursa. Nachfolgende Studien zur Rezeptorontogenese ergaben eine deutliche positive Korrelation zwischen der Expression des Zytokinrezeptors und derjenigen des B-Zellrezeptors in der embryonalen Bursa. Im Rezeptor-Ligand-Interaktions-ELISA konnte ebenso wie durch Ko-Immuno-präzipitation eine Bindung von chBAFF an alle drei bislang bekannten BAFF-Rezeptoren des Säugers gezeigt werden. Von besonderer Bedeutung war hierbei, dass die chBAFF-Bindung an die Hühner-B-Zelllinie DT40 durch eine lösliche Variante des humanen BAFF-Rezeptors BCMA (huBCMA-Fc) blockiert werden konnte. Der Zusatz von eukaryotisch exprimiertem chBAFF zu Kulturen aus Milzlymphozyten führte zu einem signifikanten Anstieg der Zahl lebender B-Zellen. Dieser dosisabhängige Effekt war auch in Lymphozytenkulturen aus Caecaltonsillen und in Kulturen gereinigter (>95%) B-Zellpräparationen aus der Milz zu beobachten. Die rasche Apoptose bursaler Lymphozyten in Kultur konnte zwar nicht gänzlich verhindert werden, die Supplementierung von chBAFF führte aber auch in Kulturen dieser unreifen B-Zellen zu einer deutlichen Zunahme der Viabilität. Anschließende Experimente mit CFSE markierten Zellen ergaben, dass chBAFF nicht zur Proliferation der B-Zellen führt. Die nachgewiesenen Effekte werden folglich mit großer Wahrscheinlichkeit durch die potente Inhibition der Apoptose der B-Zellen verursacht. Die Zellkulturarbeiten konnten durch in vivo Studien mit gereinigtem prokaryotischem chBAFF bestätigt werden. Die tägliche Injektion des rekombinanten Zytokins über sieben Tage hinweg induzierte dabei eine signifikante Zunahme von Milzgewicht und B-Zellfrequenz in Milz und Caecaltonsillen. Zusätzlich kam es durch die funktionelle chBAFF-Überexpression zu einem signifikanten (4-fachen) Anstieg der IgM-Serumspiegel. Somit scheint chBAFF nicht nur die Zahl der B-Zellen zu beeinflussen, sondern auch deren Differenzierung zu Antikörper sekretierenden Zellen. Da durch die Supplementierung des Zytokins keine Effekte auf die Bursa erzielt werden konnten, wurde nachfolgend der umgekehrte experimentelle Ansatz gewählt und endogenes chBAFF bei frisch geschlüpften Küken fünf Tage lang durch die tägliche i.p. Injektion von huBCMA-Fc neutralisiert. Dieser funktionelle Knockdown führte zur Abnahme des Milzgewichts und einer drastischen Reduktion der B-Zellfrequenz in Milz und Caecaltonsillen. Zudem konnte eine Verringerung der Bursagewichte beobachtet werden. Dieser Befund, sowie die vorrangige chBAFF-mRNA-Expression in der Bursa und die Expression seiner Rezeptoren auf bursalen B-Zellen, deuten zusammengenommen auf eine bislang unbekannte Rolle von BAFF in der frühen B-Zellentwicklung hin

Chicken BAFF

Members of the tumor necrosis factor (TNF) family play key roles in the regulation of inflammation, immune responses and tissue homeostasis. Here we describe the identification of the chicken homologue of mammalian B cell activating factor of the TNF family (BAFF/BLyS). By searching a chicken EST database we identified two overlapping cDNA clones that code for the entire open reading frame of chicken BAFF (chBAFF), which contains a predicted transmembrane domain and a putative furin protease cleavage site like its mammalian counterparts. The amino acid identity between soluble chicken and human BAFF is 76%, considerably higher than for most other known cytokines. The chBAFF gene is most strongly expressed in the bursa of Fabricius. Soluble recombinant chBAFF produced by human 293T cells interacted with the mammalian cell-surface receptors TACI, BCMA and BAFF-R. It bound to chicken B cells, but not to other lymphocytes, and it promoted the survival of splenic chicken B cells in culture. Furthermore, bacterially expressed chBAFF induced the selective expansion of B cells in the spleen and cecal tonsils when administered to young chicks. Our results suggest that like its mammalian counterpart, chBAFF plays an important role in survival and/or proliferation of chicken B cells

Chicken Toll-like Receptor 3 Recognizes Its Cognate Ligand When Ectopically Expressed in Human Cells

Recognition of pathogens by toll-like receptors (TLRs) causes activation of signaling cascades that trigger cytokine secretion and, ultimately, innate immunity. Genes encoding proteins with substantial homology to mammalian TLR1, TLR2, TLR3, TLR4, TLR5, and TLR7 are present in the chicken genome, whereas orthologs of TLR8, TLR9, and TLR10 seem to be defective or missing. Except for chicken TLR2 (ChTLR2), which was previously shown to recognize lipopeptides and lipopolysaccharides (LPS), the ligand specificity of ChTLRs had not been determined. We found that polyI:C, LPS, R848, S-28463, and ODN2006, which are specifically recognized by TLR3, TLR4, TLR7/8, and TLR9 in mammals, induced substantial amounts of type I interferon (IFN) and interleukin-6 (IL-6) in freshly prepared chicken splenocytes. To determine the ligand specificity of ChTLR3 and ChTLR7, we used a standard reporter assay frequently employed for analysis of mammalian TLRs. Neither S-28463 nor any other TLR ligand induced reporter activity in human 293 cells expressing ChTLR7. However, human 293 cells expressing ChTLR3 strongly and specifically responded to polyI:C, demonstrating that this chicken receptor represents a true ortholog of mammalian TLR3

Avian Bornaviruses Escape Recognition by the Innate Immune System

Like other pathogens that readily persist in animal hosts, members of the Bornaviridae family have evolved effective mechanisms to evade the innate immune response. The prototype of this virus family, Borna disease virus employs an unusual replication strategy that removes the triphosphates from the 5′ termini of the viral RNA genome. This strategy allows the virus to avoid activation of RIG-I and other innate immune response receptors in infected cells. Here we determined whether the newly discovered avian bornaviruses (ABV) might use a similar strategy to evade the interferon response. We found that de novo infection of QM7 and CEC32 quail cells with two different ABV strains was efficiently inhibited by exogenous chicken IFN-α. IFN-α also reduced the viral load in QM7 and CEC32 cells persistently infected with both ABV strains, suggesting that ABV is highly sensitive to type I IFN. Although quail cells persistently infected with ABV contained high levels of viral RNA, the supernatants of infected cultures did not contain detectable levels of biologically active type I IFN. RNA from cells infected with ABV failed to induce IFN-β synthesis if transfected into human cells. Furthermore, genomic RNA of ABV was susceptible to 5′-monophosphate-specific RNase, suggesting that it lacks 5′-triphospates like BDV. These results indicate that bornaviruses of mammals and birds use similar strategies to evade the host immune response

Chicken BAFF—a highly conserved cytokine that mediates B cell survival

Members of the tumor necrosis factor (TNF) family play key roles in the regulation of inflammation, immune responses and tissue homeostasis. Here we describe the identification of the chicken homologue of mammalian B cell activating factor of the TNF family (BAFF/BLyS). By searching a chicken EST database we identified two overlapping cDNA clones that code for the entire open reading frame of chicken BAFF (chBAFF), which contains a predicted transmembrane domain and a putative furin protease cleavage site like its mammalian counterparts. The amino acid identity between soluble chicken and human BAFF is 76%, considerably higher than for most other known cytokines. The chBAFF gene is most strongly expressed in the bursa of Fabricius. Soluble recombinant chBAFF produced by human 293T cells interacted with the mammalian cell‐surface receptors TACI, BCMA and BAFF‐R. It bound to chicken B cells, but not to other lymphocytes, and it promoted the survival of splenic chicken B cells in culture. Furthermore, bacterially expressed chBAFF induced the selective expansion of B cells in the spleen and cecal tonsils when administered to young chicks. Our results suggest that like its mammalian counterpart, chBAFF plays an important role in survival and/or proliferation of chicken B cell

Unique and conserved functions of B cell-activating factor of the TNF family (BAFF) in the chicken

The chicken represents the best-characterized animal model for B cell development in the so-called gut-associated lymphoid tissue (GALT) and the molecular processes leading to B cell receptor diversification in this species are well investigated. However, the mechanisms regulating B cell development and homeostasis in GALT species are largely unknown. Here we investigate the role played by the avian homologue of B cell-activating factor of the tumor necrosis factor family (BAFF). Flow cytometric analysis showed that the receptor for chicken B cell-activating factor of the tumor necrosis factor family (chBAFF) is expressed by mature and immature B cells. Unlike murine and human BAFF, chBAFF is primarily produced by B cells both in peripheral lymphoid organs and in the bursa of Fabricius, the chicken's unique primary lymphoid organ. In vitro and in vivo studies revealed that chBAFF is required for mature B cell survival. In addition, in vivo neutralization with a decoy receptor led to a reduction of the size and number of B cell follicles in the bursa, demonstrating that, in contrast to humans and mice, in chickens BAFF is also required for the development of immature B cells. Collectively, we show that chBAFF has phylogenetically conserved functions in mature B cell homeostasis but displays unique and thus far unknown properties in the regulation of B cell development in bird

Acute paretic syndrome in juvenile White Leghorn chickens resembles late stages of acute inflammatory demyelinating polyneuropathies in humans

Background: Sudden limb paresis is a common problem in White Leghorn flocks, affecting about 1% of the chicken population before achievement of sexual maturity. Previously, a similar clinical syndrome has been reported as being caused by inflammatory demyelination of peripheral nerve fibres. Here, we investigated in detail the immunopathology of this paretic syndrome and its possible resemblance to human neuropathies. Methods: Neurologically affected chickens and control animals from one single flock underwent clinical and neuropathological examination. Peripheral nervous system (PNS) alterations were characterised using standard morphological techniques, including nerve fibre teasing and transmission electron microscopy. Infiltrating cells were phenotyped immunohistologically and quantified by flow cytometry. The cytokine expression pattern was assessed by quantitative real-time PCR (qRT-PCR). These investigations were accomplished by MHC genotyping and a PCR screen for Marek’s disease virus (MDV). Results: Spontaneous paresis of White Leghorns is caused by cell-mediated, inflammatory demyelination affecting multiple cranial and spinal nerves and nerve roots with a proximodistal tapering. Clinical manifestation coincides with the employment of humoral immune mechanisms, enrolling plasma cell recruitment, deposition of myelinbound IgG and antibody-dependent macrophageal myelin-stripping. Disease development was significantly linked to a 539 bp microsatellite in MHC locus LEI0258. An aetiological role for MDV was excluded. Conclusions: The paretic phase of avian inflammatory demyelinating polyradiculoneuritis immunobiologically resembles the late-acute disease stages of human acute inflammatory demyelinating polyneuropathy, and is characterised by a Th1-to-Th2 shift