Immunological responses following early embryonic surgical bursectomy

Hormonal and late embryonic surgical bursectomy have been shown to produce chicks deficient in IgM and/or IgG, depending on the time of bursectomy. Some of these hormonally bursectomized birds were reported to have atrophy of the thymic cortex.We have developed a new technique for early embryonic surgical bursectomy (at 70 hr in ovo). Results of stimulation tests with BSA and SRBC indicates a few of the bursectomized birds are capable of producing small amounts of antibody. Early embryonic surgical bursectomy also results in incomplete development of the thymic cortex, indicating a developmental interrelationship exists between the bursa and thymus.     

Immune capacity of the chicken bursectomized at 60 hr of incubation: surface immunoglobulin and B-L (La-like) antigen-bearing cells

Chickens were surgically bursectomized at 60 hr of incubation before the bursal anlage appears. Completeness of the bursectomy was confirmed at autopsy at 10 wk of age. These embryonically bursectomized (Bx) chickens are known to produce immunoglobulins of IgM, IgG, and IgA classes, but so far no specific antibodies have been observed even after heavy immunization. Regarding the appearance of surface immunoglobulin positive (s-Ig+) cells, the most striking effect of bursectomy was observed in the frequency of s-IgG+ cells, which were markedly decreased in the spleen, peripheral blood, and thymus of the Bx birds when compared with the age-matched controls. s-IgM+ cells were significantly decreased in the peripheral blood and s-IgA+ cells in the spleen of the Bx birds. In contrast to these findings, s-Ig+ cells of all three classes were present in normal frequency in the bone marrow. Bursectomy had no effect on the total lymphocyte and other white cell counts in the peripheral blood. Likewise, no effect on the frequency of B-L (Ia-like) antigen-positive cells in different organs was observed.     

Thymic development in surgically bursectomized embryonic chicken: expression of PCNA, CD3, CD4 and CD8 markers

Little information is available on the functional relationship between bursa and thymus during chicken embryogenesis. We, therefore, investigated embryonic thymuses taken at 17 days in ovo from chickens bursectomized at 68-72 hours, with histological, histochemical (PAS, Alcian blue), and immunoreaction (anti-cytokeratin B, anti-PCNA/cyclin and anti-CD3, CD4 and CD8 antibodies) methods and compared these data with those from normal and sham-operated chickens of the same age. The bursectomized thymuses distinctly differed from normal and sham-operated thymuses: they were smaller, and the cortical zone was thinner and contained fewer epithelial cells and thymocytes. Only few cortical thymocytes were immunoreactive for PCNA, indicating low proliferative rate. More cortical thymocytes as compared with the normal, expressed CD3 on their cell membrane, whereas the thymocytes at the cortical-medullary border expressing anti- CD4 and anti-CD8 antidodies were less numerous than in normal thymus. The medullary zone contained few epithelial clusters made up of fewer cells than medullary clusters in normal chickens. Some cystic formations were enlarged and contained PAS- or Alcian-blue positive amorphous material. All these data suggest that early bursectomy affects both morphological and functional thymic development.     

A novel method to bursectomize avian embryos and obtain quail----chick bursal chimeras. II. Immune response of bursectomized chicks and chimeras and post-natal rejection of the grafted quail bursas

Two methods to bursectomize chick embryos before hemopoietic cell seeding of the bursa of Fabricius were compared in this work: section of the tail region at E3 including the presumptive bursal territory, and selective removal of the bursa at E5. Hatching ability is better with the former method, but survival rate and effectiveness of bursectomy are favored with the second, novel technique. Moreover, selective removal of the bursa at E5 can be followed by in situ engraftment of a quail bursa and construction of quail-chick bursal chimeras. The immune response of bursaless birds and bursal chimeras has been studied. Total absence of the bursa does not prevent a few B cells from differentiating and nonspecific Ig (IgM and/or IgG) from being secreted. As reported previously, bursaless birds, however, are unable to mount an immune response by producing specific antibodies. This immune function is restored by the graft of a quail bursa. The microenvironment of the bursa, although heterospecific, allows the expansion of the B cell population and generates the repertoire of the B cell antigen receptors. This process takes place during late embryonic and early postnatal life because the grafted quail bursal stroma is subjected to immune rejection from 2 to 3 wk after birth in all chimeras, which are, however, perfectly immunocompetent.     

Cytochemical examination of peripheral blood lymphocytes in bursectomized chickens

The starting material were 86 day-old utility hybrid Tetra SL chicks. Beginning from their third week of life, 59 chickens were kept in two separate rooms "A" and "B" for 42-56 days. The values of temperature and cooling were somewhat different in rooms "A" and "B", however essentially not deviating from the accepted zoohygienic norms. The obtained results revealed a significant reduction of the activity of acid phosphatase in blood lymphocytes of 8-10 week-old chickens bursectomized in the neonatal period and kept in room "A". No such changes were found concerning ATP-ase and 5'-nucleotidase. Similar effect appeared in the lymphocytes of non-bursectomized chickens kept in room "B". Antigen stimulation (SRBC) of bursectomized and non-bursectomized chickens brought about an increased activity of all the three enzymes in blood lymphocytes. At the same time it should be emphasized that the increased activity of the enzymes tested was modulated by bursectomy and conditions of the medium.     

Bursectomy in ovo blocks the generation of immunoglobulin diversity.

Immunoglobulins made by chickens bursectomized in ovo on day 11 of incubation were studied by two-dimensional gel electrophoresis. All such bursectomized chickens have limited diversity in their immunoglobulin molecules. A range of different degrees of diversity restriction was found in individual bursectomized chickens. The limited immunoglobulin diversity was stable for at least 20 weeks in that the same spots were found over this time span. Bursectomized chickens that responded to repeated antigen challenge had sheep erythrocyte- and dinitrophenol-specific antibodies of limited diversity. Different bursectomized responders made almost identical antigen-specific antibodies. The results were interpreted as indicating that individual bursectomized birds had been blocked at different points during the developmental generation of immunoglobulin diversity, and that the genetic mechanisms that underlie the developmental diversification of clones of B cells lead to a sequential generation of very similar antibody molecules in different embryos.     

Development of blood testosterone in the embryo and young chick after precocious bursectomy

The effect of bursa of Fabricius on the endocrine function of the chick testes was studied in vivo by comparing plasma testosterone levels from 48 h before hatch to 16 weeks of age in both intact and bursectomized chicken. Early bursectomy was performed at 80 h of incubation. Post surgery survival was low (12% at 1 week). In controls, plasma testosterone levels were found to be low (100-200 pg. ml-1) from 48 h before to 48 h after hatch, then to raise up to a plateau (2,200 pg. ml-1) at 6 weeks. After bursectomy, values were first higher than in intact (210-440 pg. ml-1 from 48 h before/after hatch and 515 vs 300 pg.ml-1 at 3 days) but no difference could be further detected from 1 to 16 weeks of age. It is suggested that, in addition to the effect of androgen on bursa of Fabricius, the later reciprocally influences the gonadotropic axis during the early stage of development.     

A novel method to bursectomize avian embryos and obtain quail----chick bursal chimeras. I. Immunocytochemical analysis of such chimeras by using species-specific monoclonal antibodies

Chick embryos were bursectomized at 5 days of incubation according to a novel surgical technique described in this article. This method yields birds that are able to hatch and are devoid of the physiologic deficiencies resulting from the previously used method, which involved resection of the cloacal and posterior embryonic region. The bursectomized embryos were grafted in situ with a quail bursa of the same age, which thereafter became chimeric through chick host hemopoietic cell invasion. By means of species-specific antibodies, the chimeric condition revealed 1) that the bursal epithelium expresses a unique antigenic determinant (MB1 determinant), until now considered to be an exclusive feature of blood vessel endothelium and hemopoietic cells, and 2) that this determinant appears in bursal epithelium at the time and site of hemopoietic cell invasion. The other point arising from this work concerns the apparent constitutive Ia expression by perifollicular blood capillary endothelial cells in normal and chimeric bursas.     

Comparison of plasma ACTH and corticosterone levels after embryo bursectomy

Plasma levels of both adrenocorticotropic hormone (ACTH) and corticosterone (B) were determined in embryos (day 15 of incubation), chicks (day 3 after hatch) and young chickens (8 weeks). Experimental animals were bursectomized at 80 hr of incubation, i.e., before any anlage of the bursa of Fabricius could develop. Bursectomized (BFX) animals were compared to sham-operated controls (T), in basal, resting condition and 7 (ACTH) or 14 min (B) after ether stress was delivered for 30 sec. Basal B and ACTH levels seemed not to be significantly modified in BFX embryos, chicks and chickens. Hypophysial and adrenocortical response to stress appeared more precociously in BFX embryos (day 15 of incubation) than in intact ones (day 19). The non stress-responsive period that was observed for one week after hatch of T birds did not appear in 3-day-old BFX chicks whose both B and ACTH stress-induced levels were as high as in intact adults. In contrast, adrenocortical and pituitary corticotropic responses to stress were markedly impaired (by 50%) in adult BFX chickens as compared to intact controls.     

Defective bursa regeneration after irradiation of young thymectomized chickens

The ability of the bursa of Fabricius to regenerate after gamma-irradiation and bone marrow reconstitution was examined in chickens thymectomized (TX) immediately after hatching. Irradiation (2 X 500 R) 3 weeks after hatching was followed by impaired bursa regeneration, as judged both by bursa/body weight ratios and by bursa follicle development 3-6 weeks later in TX as compared to control birds. Germinal center formation in the spleen was deficient, and immune responses to sheep erythrocytes (SRBC) and B. abortus (BA) were moderately reduced in the TX as compared to control birds irradiated at 3 weeks but not in TX birds irradiated at 5 weeks of age.     

Investigation of the site of precursors for IgA-producing cells in the chicken intestine

Bursectomized chicks received lymphocyte single cell suspensions harvested from the bursa of Fabricius (BF), ileal lymphoid aggregate (ILA), caecal tonsils (CT), spleen and peripheral blood. Four days after cell transfer, repopulation of the duodenal and CT lamina propria in age-matched recipient bursectomized chickens with IgA-secreting plasma cells was determined. The results indicate the highest level of reconstitution with cells derived from BF, but substantial numbers of IgA-secreting plasma cells were also observed in a number of birds that received lymphocytes originating from the ILA and CT.     

Effect of bursectomy and thymectomy on cellular immunological reactions in chickens

The effect of thymectomy + irradiation and of bursectomy + irradiation on the rejection of skin grafts and injected homologous spleen cells was studied. Prolonged skin graft survival was found in thymectomized and irradiated chickens. Bursectomy together with irradiation and isolated irradiation did not affect the rejection of these grafts. Surgical operations together with irradiation had no effect on the rejection of an allogenein cellular graft. In one-day-old recipients, survival of the cells was prolonged in all the birds, while in 12-day-old recipients the cells were rejected at the normal time by both bursectomized and thymectomized birds. The possible explanations of these results are discussed. Dedicated to Academician Ivan Málek on the occasion of his 60th birthday     

Evidence for the presence of precursor B cells in normal and in hormonally bursectomized chick embryos

Embryonic bone marrow of normal and hormonally bursectomized chicks was examined for the presence of hematopoietic precursor cells capable of migrating to the thymus and bursa and of differentiating into functional T and B cells, respectively. Following transfer of chromosomally marked bone marrow of normal and in ovo bursectomized 14-day-old embryos to 14-day-old γ-irradiated embryonic recipients, donor cells proliferated in the marrow, thymus, and bursa of recipients, and differentiated to PHA- and Con A-responsive T cells as well as to dextran sulfate- and anti-immunoglobulin-responsive B cells. In contrast, when marrow of 2-day-old hatched normal and in ovo-bursectomized donors was transferred to 14-day-old embryonic recipients, donor cells repopulated only the marrow and thymus of recipients which was followed by differentiation to Con A- or PHA-responsive T cells, but the same donor cells failed to proliferate in the bursa and there was no differentiation to functional B cells of donor type. The data were fitted to a model of T- and B-cell differentiation from the stem cell level and they suggest the presence of separate populations of committed precursor T (PT) and precursor B (PB) cells in the marrow of normal and in ovo bursectomized embryos with a bursa-independent selective disappearance of PB cells from the marrow during the late embryonic period.     

Transfer of agammaglobulinemia in the chicken. I. Generation of suppressor activity by injection of bursa cells

Spleen cells from adult agammaglobulinemic (bursectomized) chickens taken 1 to 3 weeks after an injection of histocompatible bursa cells can inhibit the adoptive antibody response to B. abortus of normal spleen or bursa cells in irradiated recipients. Spleen cells from Aγ chickens not injected with bursa cells generally do not. Moreover, bursectomized chickens which have been reconstituted with spleen cells within the first week after hatching do not respond with suppressor cell formation upon bursa cell injection. This apparent “autoimmunization” with bursa cells induces suppressor T cells which are only minimally sensitive to treatment with mitomycin C or to 5000 R γ irradiation. The suppressor activity is neither induced nor potentiated by concanavalin A in vivo. It is much stronger in spleen than in thymus cells and appears to be macrophage independent and to require intact cells. The cell component which stimulates the suppressor activity is more pronounced on bursa than on spleen cells, and is at most present to a very limited extent on bone marrow, thymus, or peritoneal exudate cells. It is better represented in comparable cell numbers of Day 17 than of Day 14 embryonic bursa. The inducing cell component is present in the membrane fraction of disrupted bursa cells. Immunization with bursa cells from B locus histoincompatible chickens leads to suppressor activity against histocompatible bursa cells. Although the removal of Ig-bearing cells from bursa greatly diminishes its immunizing capacity, injection of serum IgM and IgG does not induce suppressor cells. It is suggested that tolerance to a B-cell antigen is lacking in adult Aγ chickens, resulting in an autoimmune response upon exposure to B cells. The B-cell antigen may be a cell surface-specific form of Ig, a complex of Ig and a membrane component, or a differentiation antigen which appears simultaneously with Ig during ontogeny.     

Persistence of abnormal melanocytes in immunosuppressed chickens of the autoimmune “DAM” line

Summary The delayed amelanotic (DAM) line of chickens (Gallus gallus) is characterized by the postnatal elimination of melanocytes from regenerating feathers and from the choroid. The process of elimination is accompanied by a massive infiltration of mononuclear leukocytes (MNL) into the supporting connective tissues. When surgically bursectomized at day of hatching, chickens from this lineage develop significantly less amelanosis of the feathers. We report here a histological analysis of regenerating feathers and choroids from bursectomized birds that maintained their plumage pigmentation. In the feathers we observed the presence of morphologically abnormal melanocytes in the absence of MNL infiltration. Choroids also contained abnormal melanocytes without MNL infiltration; however, we observed a few cases of amelanotic choroids with a few MNL. These findings indicate that melanocytes of pigmented birds are morphologically abnormal even in the absence of a bursa and in the absence of leukocytic infiltrates into regenerating feathers and possibly into the choroids. We conclude from these findings that the amelanosis in unbursectomized DAM birds is due to the response of the immune system to an abnormality in the melanocytes which, by itself, does not lead to depigmentation.     

Bursectomy of chicken embryos at 60 hours of incubation leads to an oligoclonal B cell compartment and restricted Ig diversity

Chickens that have been surgically bursectomized at 60 h of embryonic development usually generate Ig producing B cells; however, the bursectomized chickens are incapable of specific antibody responses, even after repeated immunization. In the present work, we analyzed the molecular basis of this immunodeficiency. In the bursectomized chickens, DNA sequencing revealed a repertoire of Ig L and H chains with a low number of different V-J and V-D-J joints, indicating an oligoclonal B cell compartment. In addition, the L and H chains belonging to each B cell clone had similar gene conversion events in the V region. In situ hybridization to Harderian gland tissue sections showed, that B cells of the bursectomized chickens were, however, capable of terminal plasma cell maturation. Thus, in chickens that were lacking the bursal microenvironment, 1) only a few B cell precursors differentiated into mature Ig-producing B cells, 2) low rate of gene conversion resulted in restricted Ig diversity. Regarding the chicken B cell differentiation, the present data support a model that the induction of B cell differentiation is a bursa-independent event, whereas the bursa of Fabricius has a crucial role in the amplification and diversification of the embryonic B cell repertoire.     

Ia-like alloantigens in the chicken: Serologic characterization an ontogeny of cellular expression

Alloantisera raised in highly inbred lines of chickens, 7(2) and 15I(5) , by reciprocal immunization with lymphocytes were shown by immunofluorescence to react with B cells, cells of the monocyte-macrophage series, and an unidentified population of mononuclear cells prevalent in the spleen and bone marrow. Variable immunogenicity of the 'Ia'(2) and 'Ia'(15) alloantigens was observed. The alloantigens detected by these sara could be redistributed on the B-cell surface independently of immunoglobulin determinants or previously recognized antigens encoded by the major histocompatibility complex (B locus), and were more resistant to proteolysis than slgM. Analysis of several inbred lines of chickens revealed an association between expression of these antigens and the B haplotype. Strains of the B(2) haplotype expressed the antigen detected by anti-7 2 and vice versa. These data suggest that the B-cell alloantigens detected are encoded by genes linked to the MHC and may be analogous to la antigens of mice and DR antigens of man. 'Ia' alleles were co dominantly expressed on lymphocytes of F(1) hybrids. During ontogeny 'a'(+) cells were first detected in the bursa at 10 days of incubation , 3 days before 'Ia'(+). IgM(+) cells could be detected. Both 'Ia'(+).IgM(+) and 'Ia'(+).IgM(-) populations of bursal cells increased in parallel until day 18, when plateau levels were reached. Development of 'Ia'(+).IgM(-) cells throughout the body was unaffected by bursectomy at hatching. Cell surface expression of 'Ia' antigens was apparently increased with B-Iymphocyte maturation and was detectable on most, but not all, mature plasma cells.     

High RAD51 mRNA levels in young rabbit appendix. A role in B-cell gene conversion?

 The rabbit has a limited number of V _H genes that rearrange. As in the chicken, the 3′-most V _H 1 gene is rearranged in most B lymphocytes. This laboratory reported that by 6 weeks after birth, diversification of rearranged V _H genes occurs, at least in part, by gene conversion-like events in the appendix, suggesting that this organ is a homologue of the avian bursa of Fabricius. Rad51 contributes to the repair of double-strand breaks in DNA during somatic and meiotic recombination. The gene was first identified in lower eukaryotes, and later in vertebrates including chicken, as encoding an Escherichia coli RecA-like protein. We report the cloning and sequencing of RAD51 from the rabbit. Because the chicken bursa was shown to express high levels of RAD51 message, we investigated the expression of RAD51 in the rabbit appendix and other tissues. Using a quantitative polymerase chain reaction mimic assay and conventional northern analyses, we found high RAD51 expression in young rabbit appendix comparable to levels in testis where there is an abundance of meiotic recombination. RAD51 levels were three times higher in appendix B lymphocytes compared with T lymphocytes and were lower in adult appendix, as well as in spleen and Peyer's patches of young rabbits. We measured the levels of message in several appendix cell sub-populations obtained by fluorescence-activated cell sorting and found that sub-populations of B lymphocytes corresponding to different stages of B-cell development as well as B cells undergoing isotype switch did not have significantly different mRNA levels. Received: 18 October 1997 / Revised: 10 December 1997     

Ascaridia galli: effects of immunosuppressive drugs or bursectomy in chickens

Immunosuppressive drugs significantly increasing numbers of A. galli and incidences of infection were: cortisone, cortisol, 9-α-fluorohydrocortisone, 2-methyl-9-α-fluorohydrocortisone, prednisone, prednisolone, 6-mercaptopurine, 2, 6-diaminopurine, 6-thioguanine, 5-bromodeoxyridine, 5-fluorouracil, methotrexate, chlorambucil, and actinomycin D. These drugs and/or worm burdens significantly suppressed weight gains of hosts, and neither altered the male:female ratio of worms nor their growth. The following drugs neither altered worm burdens nor increased incidences of infection: corticosterone, 2-azaadenine, 8-azaguanine, azathioprine, 6-azauridine, busulfan, thio-TEPA, triethylenemelamine, vincristine, acriflavine, reserpine, and l-phenylalanine.Worm burdens and incidences of infection were increased significantly in chickens surgically bursectomized when 3 or 14 but not 35 days old. Chicks bursectomized in ovo with testerosterone propionate on Day 5 or 14 of incubation and infected on Day 14 after hatching developed significantly increased worm burdens and incidences of infection.Applying the Kolmogorov-Smirnov test for goodness of fit to data on increased worm burdens showed that the immunosuppressive drugs or bursectomy had a normalization effect on the statistical distribution.     

Sequential expression of germ line genes in development of immunoglobulin class diversity.

Differentiation of B cells occurs in two discontinuous stages. Primary differentiation of stem cells to B lymphocytes in birds occurs exclusively in the lymphoepithelial bursa of Fabricius; the fetal liver may serve this function in mammals. In chickens both the size of the B-lymphocyte pool and the generation of precursors for cells secreting different immunoglobulin classes is controlled by the bursa. The latter process involves the sequential expression of genes coding for heavy chain constant regions in the order mu, gamma, alpha. The second stage of B-cell differentiation is antigen-driven, and involves proliferation and maturation of B lymphocytes to plasma cells. Ontogenetic development of different classes of B lymphocytes in mammals is orderly, independent of exogenous antigens, and occurs in the sequence mu, gamma, alpha. A developmental switch in expression of Ch genes, beginning with mu, has been experimentally verified. We favor the hypothesis that generation of class diversity of B lymphocytes occurs during the antigen-independent first stage of differentiation, and that the genetic switch in Ch gene expression follows the sequence mu leads to gamma leads to alpha, but evidence of these points remains inconclusive.