Suppression of adoptive antibody responses by addition of spleen cells from agammaglobulinaemic chickens "immunised" with histocompatible bursa cells

The Discovery of Chicken Foxp3 Demands Redefinition of Avian Regulatory T Cells

Since the publication of the first chicken genome sequence, we have encountered genes playing key roles in mammalian immunology, but being seemingly absent in birds. One of those was, until recently, Foxp3, the master transcription factor of regulatory T cells in mammals. Therefore, avian regulatory T cell research is still poorly standardized. In this study we identify a chicken ortholog of Foxp3 We prove sequence homology with known mammalian and sauropsid sequences, but also reveal differences in major domains. Expression profiling shows an association of Foxp3 and CD25 expression levels in CD4⁺CD25⁺ peripheral T cells and identifies a CD4^-CD25⁺Foxp3^high subset of thymic lymphocytes that likely represents yet undescribed avian regulatory T precursor cells. We conclude that Foxp3 is existent in chickens and that it shares certain functional characteristics with its mammalian ortholog. Nevertheless, pathways for regulatory T cell development and Foxp3 function are likely to differ between mammals and birds. The identification and characterization of chicken Foxp3 will help to define avian regulatory T cells and to analyze their functional properties and thereby advance the field of avian immunology.

Contemporary models for peripheral tolerance and the classical 'historical postulate'

The formulators of Clonal Selection Theory proposed that what distinguishes self from foreign antigens is their early appearance in development, and their continuous presence thereafter. This early presence of a self antigen in an animals life history was envisaged to ensure that lymphocytes specific for the self antigen were silenced rather than activated. I call this idea 'the historical postulate'. Contemporary models for the activation/inactivation of helper T cells implicitly violate this postulate. I argue against such a violation and for a model of T helper cell activation/inactivation that reconciles contemporary observations with the postulate.

Pre-B cells in agammaglobulinemia: evidence for disease heterogeneity among affected boys

Six immunodeficient boys were found to have agammaglobulinemia and lack circulating B cells. These patients could be divided into two groups based on bone marrow findings and clinical course. In one group, pre-B cells and lymphocytes were present at normal frequencies and in normal absolute numbers. Recurrent serious infections were documented in the first few months of life in these patients, and this consequently led to early diagnosis. In the second group, pre-B cells were virtually undetectable. Patients in this group did not present with recurrent infections until the second year and were thus diagnosed later than were those in the first group. Childhood agammaglobulinemia with deficiency of both pre-B and B lymphocytes appears to be a different disease from X-linked infantile agammaglobulinemia. This disease may involve an arrest of B-lineage cell development at an earlier stage than that responsible for X-linked agammaglobulinemia.

Immune responsiveness and lymphoreticular morphology in cattle fed hypo- and hyperalimentative diets

Immune responses and lymphoreticular morphology were studied in 3 groups of yearling Hereford steers fed hypoalimentative, maintenance and hyperalimentative diets for 142 days. Significant decreases in plasma protein levels and circulating lymphocyte levels occurred in low energy intake steers. Percent circulating lymphocytes bearing surface immunoglobulins and serum levels of IgG and IgM did not vary significantly within or between groups. Antibody responses to Brucella abortus bacterin inoculated on day 63 were similar in all 3 groups. Antibody responses to chicken erythrocytes inoculated on day 88 were significantly lower in hypoalimentated steers. Differences between groups in lymphocyte blastogenic responses to phytohemagglutinin (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM) were not significant. Hyperalimentated steers had significantly depressed PWM responses compared to a baseline value established for that group. In addition, hypoalimentated steers tended to have elevated responses to PHA, although differences were not significant. There were no significant differences between groups in dermal hypersensitivity responses to tuberculin following sensitization with viable Bacillus Calmette-Guerin (BCG). The thymuses of hypoalimentated steers were markedly atrophied but lymph nodes and splenic white pulp were normal. Thymus, lymph nodes and spleen were normal in hyperalimentated steers.

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.

Effects of anti-T lymphocyte serum on immunological reactivity and on the T cell area of the cloacal bursa in the chicken

The effects of rabbit anti-chicken T-lymphocyte serum (RACTS) on the immune response in chickens stimulated either locally (per anum) or systemically (i.p.) with sheep red blood cells (SRBC; T-cell-dependent antigen) as well as on the morphological characteristics of the diffusely infiltrated area (DIA; T-cell region of the bursa) were studied. Antibody response to SRBC was measured by the serum anti-SRBC agglutination titres. In the DIA, the percentages of T cells, B cells and macrophages (MPS cells) were counted, and the different parameters of the post-capillary venules (PCVs) determined morphometrically. The response to SRBC was very significantly impaired in locally immunized chickens treated systemically with RACTS. In the DIA, the relative number of T cells was dramatically decreased, as was, although less drastically, that of MPS cells. In chickens immunized locally with SRBC, RACTS caused strong morphological alterations in the PCVs of the DIA; decrease in the diameter of the PCV and its lumen and flattening of the endothelial cells. The migration index did not significantly decrease due to the RACTS treatment. Following the systemic immunization with SRBC, no changes in the morphology of the PCVs attributable to the RACTS treatment could be observed. The present results give further support to the concept of the structural and functional analogy between the chicken cloacal bursa and the mammalian gut-associated lymphoid tissue (GALT) and the lymph nodes, thus strongly favouring the idea of the bursa functioning like a peripheral lymphatic organ.

Subpopulations of suppressor cells in chickens infected with cells of a transplantable lymphoblastic leukemia

Three distinct subpopulations of cells with suppressor activity were separated by Ficoll density gradient centrifugation methods from the spleens of 3- to 4- week-old chickens infected with cultured lymphoblastoid cells (JM-VLC), derived from JM-V leukemia: (i) a subpopulation of nonadherent cells, which separated in the T-cell-rich gradient fraction of leukemic chicken spleen, inhibited proliferative responses to concanavalin A in mixed cultures with normal chicken spleen cells; (ii) phagocytic cells (macrophages), which were the most effective suppressor cells of all subpopulations in the mixed culture assay, were recovered among the cells of greatest density in the spleens of both normal and leukemic chickens; (iii) JM-VLC cells in the buoyant gradient fractions of leukemic chicken spleens also effected suppression. In the later stages of lymphoproliferative disease, the number of spleen cells of buoyant density was increased, apparently as a result of infiltration of the spleens with JM-VLC cells.

Biochemical characterization of avian T lymphocyte-specific antigens

Sera from rabbits injected with quail thymocytes were absorbed on quail bursal and liver cells. The absorbed sera reacted with avian T but not B lymphocytes in an immunofluorescence assay. Material precipitated by the anti-T antisera from lysates of radioiodinated chicken or quail thymocytes was analyzed by one- and two-dimensional electrophoresis. Of two anti-T cell antisera studied in detail, one reacted mainly with a protein of an apparent molecular weight of 45 000 - 55 000, and the other with a protein of an apparent molecular weight 65 000 - 70 000. These proteins may be homologues of previously described mammalian T lymphocytes-specific antigens.

Enhancing effect of surgical bursectomy on antibody response

Effect of surgical bursectomy on antibody response was studied in chicks injected intrabursally with sheep red blood cells (SRBC) and Brucella abortus on day 2 of life and challenged intravenously with the same antigens on day 9. Bursectomy performed 2 days after the priming resulted in a significantly decreased anti-SRBC plaque-forming cell (PFC) response, whereas bursectomy performed 4 or 5 days after the priming clearly enhanced the PFC response. The enhancing effect of bursectomy on the PFC response was also observed if the priming was made intravenously. In antibody titers against SRBC the enhancing effect was observed only if a secondary and tertiary challenge was performed at the age of 28 and 36 days, respectively. Titers of Brucella antibodies were either reduced by the bursectomy (performed 2 or 4 days after the intrabursal priming) or left unaffected (bursectomy performed 5 days after the priming). These findings are discussed in relation to bursa-derived suppressor cells.

Influence of the bursa of Fabricius on the pathogenesis of Marek's disease

A series of experiments was conducted to study the influence of embryonal bursectomy (EBX) on the early and late pathogenesis of Marek's disease (MD). The early lytic infection in the lymphoid organs normally associated with oncogenic MD virus infection in intact chickens was not seen in EBX chickens. Therefore, the damage to the immune system was minimal. EBX chickens also had lower viremia levels, higher lymphocyte responses to mitogens, and a lower or delayed MD mortality when compared with intact chickens. Furthermore, it was shown that although vaccination with SB-1 by itself did not protect against a highly virulent MD transplantable tumor, the combination of EBX and vaccination gave significant protection. All these effects could be explained by an enhanced immune response in EBX birds. In contrast, the pathogenesis of nononcogenic MD virus was not influenced by EBX. The possible mechanism(s) involved in these observed effects of EBX on MD pathogenesis are discussed.

Antigen-induced helper and suppressor T cells in normal and agammaglobulinemic chickens

Spleen cells from chickens injected with sheep erythrocytes (SE) intravenously 2 to 14 days prior to culture were found to give faster and higher plaque-forming cell responses upon addition of antigen on day 2 rather than on day 0 of culture. Cell mixture experiments showed that this was due to the induction of suppressor T cells upon re-exposure to SE on day 0 of culture. Spleen cells taken on days 2 or 14, but not between days 4 and 7 after priming to SE were sensitive to suppression. The suppressor cells were resistant to gamma irradiation (1000 rd) and to mitomycin C, but were apparently lost after 2 days of culture in the absence of antigen. Pokeweed mitogen addition on day 0 of culture also induced suppressor cells, both in SE immune and in normal spleen. Similar suppressor cells were induced in cultures of primed spleen cells taken from agammaglobulinemic chickens. The response to Brucella abortus in vitro was not affected by induction of suppression for the anti-SE response. Suppression could also be shown after transfer of cell mixtures to irradiated recipients. Helper cell activity for the anti-SE response could readily be shown, both in vivo and in vitro, in primed spleen cells precultured for 2 days in the absence of antigen, and was also resistant to 1000 rd gamma irradiation and to mitomycin C.

T cell-dependent suppression of antibody production. I. Characteristics of suppressor T cells following tolerance induction

Specific immunological tolerance was induced in adult CBA mice by a single injection of deaggregated human IgG (dHGG). Spleen cells taken 7 to 42 days later, produced consistent suppression of a DNP-HGG collaborative antibody response on adoptive transfer into heavily irradiated recipients. Noncentrifuged F(ab')2 fragments of HGG were as effective as dHGG in the production of suppressor cells. Suppression was antigen-specific since HGG-tolerant cells failed to abrogate either a DNP-keyhole limpet hemocyanin collaborative response or antibody production to the noncross-reactive antigen, horse erythrocytes. Pretreatment of the tolerant cell population with anti-Thy-1 serum and complement reversed the suppressive effect. However, purified tolerant T cells obtained by passage through nylon wool or anti-Ig columns were less effective than the original spleen cells in mediating suppression. Analysis of the cell types appearing in the column effluents indicated that the reduction in suppressive activity is best explained by retention of T cells rather than macrophages. Different T cell populations, however, were retained on the two types of columns. In the case of anti-Ig columns, these consisted of Ly-2,3+, Ia+ effector cells, whereas nylon wool columns caused depletion of Ly-1,2,3+ cells which are known to act as amplifiers of suppression. Suppression could not be explained in terms of delay in differentiation of antibody-forming cell precursors since the effect persisted for up to 15 days after transfer of tolerant cells. The demonstration of a reduction in serum anti-DNP and anti-HGG antibodies excluded the possibility of antibody production in sites other than the spleen. A role for anti-carrier antibody-antigen complexes in mediating the effector phase of suppression was rendered unlikely by the finding that the suppressive effect of tolerant cells persisted in the absence of detectable anti-HGG antibody production. Effector T cells mediating suppression in this system were shown to bear the phenotype Ia+, Ly-2,3+ as judged by the effect of pretreatment with appropriate antisera and complement. They were spleen-seeking, but were not detected in the thymus or recirculating lymphocyte pool. Adult thymectomy failed to cause a significant reduction in suppressive activity by tolerant spleen cells indicating that at least a major component of the immediate precursors is not of recent thymic origin.

Delayed wattle reaction as a measure of cell-mediated immunity in the chicken

The cell-mediated immune (CMI) response to diphtheria toxoid (DT) was studied in commercial broiler breeder lines. The chickens were immunized with DT in complete Freund's adjuvant 21 days before CMI assay by delayed wattle reactivity (DWR) to DT. The DWR was shown to be a valid measure of CMI and to correlate with spleen cell migration inhibition and blastogenesis assays of CMI in vitro. In addition, each criterion of CMI was met, except for the passive transfer of DWR. These criteria were delayed timing, gross morphology, histopathology of DWR, and effect of antilymyphocytic sera on DWR. The duration of DWR over a 1-year period differed in the two lines of chickens tested. A significantly greater DWR was found in one line with all birds remaining reactive for CMI whereas in the other line 16% did not have CMI by the end of the year. The differences may reflect genetic variability within and between lines in expression of CMI.

Further characterization of the sensitizing bursa cells and of the target for suppression in the transfer of agammaglobulinemia

Presensitization of BX donors with B cells appears obligatory in order for their T cells to acquire suppressor capacity against the adoptive humoral antibody response of bursa cells to B. abortus. Although anti-Ig + C treatment of bursa cells removes their capacity to "immunize" BX chickens for suppressor activity, BX chickens cannot be sensitized for this effect by the injection of chicken IgM + IgG. Both embryonic and allogeneic bursa cells can "immunize" the T cells of BX chickens. The observation that spleen cells from BX chickens can cause absence of plasma cells and germinal centers in the spleen and mucosal lining of cecal tonsils of histocompatible recipients within 1-2 weeks after transfer suggests that the suppressor cells mediate their effect by acting directly on B cells at one or more stages during their development.