Cells In Chickens Research Articles

Cyclophosphamide metabolism in the primary immune organs of the chick: Assays of drug activation, P450 expression, and aldehyde dehydrogenase

Several diagnostic catalytic assays were used to determine whether organ-specific metabolic activation or detoxification of cyclophosphamide (CP) contributes to the selective toxicity of CP directed towards differentiating B cells as compared to T cells in the developing chicken. An assay for the alkylation of 4-[p-nitrobenzyl] pyridine (NBP) was used to assess comparative levels of CP activation products generated from microsomal preparations from liver, bursa of Fabricius (B cells), and thymus (T cells) of day-old chicks. Three catalytic assays were used to characterize and compare cytochrome P450-associated enzyme activities in neonatal hepatic and lymphoid tissues. Aldrin epoxidase (AE) was used to detect phenobarbital (PB)-inducible P450 activity. Ethoxyresorufin-O-deethylase (EROD) and aryl hydrocarbon hydroxylase (AHH) were used for the evaluation of polycyclic aromatic hydrocarbon (PAH)-inducible P450 activities in control and PB- or 3,3',4,4'-tetrachlorobiphenyl (TCB)-induced animals. Using the NBP assay, basal and PB-induced CP activation were observed using chick liver microsomes. However, no evidence of CP activation from immune organ microsomes was observed in control, PB-, or TCB-induced chicks. Basal and PB-induced AE activities were observed in thymus, but not bursa, and represented less than 1% of basal liver activity. EROD activity was detected in TCB-induced samples from both thymus and bursa, the thymus having the greater activity. Activities of aldehyde dehydrogenase (ALDH), an enzyme involved in CP detoxification, were about equal in cytosolic fractions from the bursa and thymus. These studies suggest strongly that tissue-specific differences in metabolic capacities are not the major factors governing the selective toxicity of CP directed towards differentiating B lymphocytes in vivo.

Aluminum stimulates the proliferation and differentiation of osteoblasts in vitro by a mechanism that is different from fluoride

Micromolar concentrations of aluminum sulfate consistently stimulated [3H]thymidine incorporation into DNA and increased cellular alkaline phosphatase activity (an osteoblastic differentiation marker) in osteoblast-line cells of chicken and human. The stimulations were highly reproducible, and were biphasic and dose-dependent with the maximal stimulatory dose varied from experiment to experiment. The mitogenic doses of aluminum ion also stimulated collagen synthesis in cultured human osteosarcoma TE-85 cells, suggesting that aluminum ion might stimulate bone formation in vitro. The effects of mitogenic doses of aluminum ion on basal osteocalcin secretion by normal human osteoblasts could not be determined since there was little, if any, basal secretion of osteocalcin by these cells. 1,25 Dihydroxyvitamin D3 significantly stimulated the secretion of osteocalcin and the specific activity of cellular alkaline phosphatase in the human osteoblasts. Although mitogenic concentrations of aluminum ion potentiated the 1,25 dihydroxyvitamin D3-dependent stimulation of osteocalcin secretion, they significantly inhibited the hormone-mediated activation of cellular alkaline phosphatase activity. Mitogenic concentrations of aluminum ion did not stimulate cAMP production in human osteosarcoma TE 85 cells, indicating that the mechanism of aluminum ion does not involve cAMP. The mitogenic activity of aluminum ion is different from that of fluoride because (a) unlike fluoride, its mitogenic activity was unaffected by culture medium changes; (b) unlike fluoride, its mitogenic activity was nonspecific for bone cells; and (c) aluminum ion interacted with fluoride on the stimulation of the proliferation of osteoblastic-line cells, and did not share the same rate-limiting step(s) as that of fluoride. PTH interacted with and potentiated the bone cell mitogenic activity of aluminum ion, and thereby is consistent with the possibility that the in vivo osteogenic actions of aluminum ion might depend on PTH. In summary, low concentrations of aluminum ion could act directly on osteoblasts to stimulate their proliferation and differentiation by a mechanism that is different from fluoride.

Temporal and spatial distribution of type XII collagen in high cell density culture of periosteal-derived cells

Periosteal-derived cells of young chicks have been reported to possess the potential to undergo terminal differentiation into osteogenic or chondrogenic phenotypes under high cell density culture conditions. In this culture, the temporal and spatial distribution of type XII collagen was immunocytochemically assessed using a monoclonal antibody. These high-density plated cells first formed a multilayer of fibroblast-like cells, in which type I and XII collagen were evenly distributed throughout the full thickness of the culture. With time, the top portion of the culture differentiated into bone tissue, while cells below this top layer differentiated into hypertrophic chondrocytes. In this transition, type XII collagen was temporally and spatially colocalized primarily with type I collagen: the top portion of bone layer was positive for both type I and XII collagens, whereas their staining intensity in the bottom portion decreased with time in culture. Using this antibody, type XII collagen was also found in developing embryonic chick tibiotarsus. These observations, taken together, suggest that type XII collagen production is a characteristic property of bone-forming cells.

In vitro morphological characterization of the bursal reticuloepithelial (REp) cells of chicken

The REp cells of the bursa follicle medulla of chicken were isolated in vitro. Culture of the REp cells was maintained over a period of 10 days and the cells were observed at 3 and 10 days by means of transmission electron microscopy (TEM) and immunofluorescence. The use of an anticytokeratin monoclonal antibody confirmed their epithelial nature. TEM observations showed the presence of desmosomes and tonofilaments, which are characteristic of epithelial cells. Furthermore, to some extent the cells regenerated in vitro the network they form in vivo. Though the growth rate becomes slower with time, the features of the REp cells do not significantly change.

Fowlpox vaccination: Routes of inoculation and pathological effects

Chickens were vaccinated against fowlpox via the wing web, oral route, drinking water or by aerosol. Using two inoculations of virus, at 5 and 26 days of age, protective immunity was induced in chickens which resisted challenge with a pathogenic fowlpox virus given either via the wing web or intravenously at 46 days of age. Aerosol and wing web vaccination induced slightly better protective immunity than drinking water or oral vaccination. Virus was detected in lung cells of chicks vaccinated by either oral, drinking water or aerosol routes. Virus was also recovered from the lungs of these chicks, maximum titre being obtained 6 days post vaccination. Although a marked histological reaction was present in the lung no clinical signs were observed in the chicks.

Specific Detection of Metastasized Human Tumor Cells in Embryonic Chicks by the Polymerase Chain Reaction

We have established a highly sensitive method for specific detection of metastasized human tumor cells in embryonic chicks using the polymerase chain reaction (PCR). The cells (HT‐1080 or KMST‐6) were inoculated into the chorioallantoic membrane vein of the chick embryo and DNA of each embryonic organ was extracted. Then, a human β‐globin‐related sequence (576 bp) in the DNA from the embryonic liver and lung was specifically amplified and detected by gel electrophoresis and by a specific oligonucleotide probe. The amplified fragments from the liver DNA samples increased gradually from 2 h to 7 days after HT‐1080 inoculation. On the other hand, with inoculation of non‐tumorigenic human embryonal fibroblast KMST‐6 cells, the DNA from the embryonic liver 7 days after inoculation did not show the PCR‐amplified product. This detection technique can contribute significantly to the precise detection of microscopic metastasis.

Carbohydrate recognition systems in avian sinusoidal liver cells

We studied the carbohydrate recognition systems on liver sinusoidal cells of adult chicken and 20-day-old embryos. We localized and quantified the binding sites for glycoproteins exposing terminal N-acetylglucosamine (GlcNAc), mannose and galactose (Gal) residues. Sinusoidal liver cells from animals of both ages express on their cell surfaces binding sites for GlcNAc, mannose and galactose residues, while hepatocytes bind glycoproteins with GlcNAc residues. The gold particles distribution on Kupffer cells depend on the binding sites and the age considered. Binding sites for GlcNAc and Gal residues are generally present as clusters of gold granules, while mannose-specific binding sites are always as single gold granules. Ligand-gold complexes bound on endothelial cells are always present on the coated regions of the cell surface. The number of GlcNAc and Gal-specific receptors expressed on the cell surface of Kupffer cells undergoes modifications between embryonal and adult life.

The use of monoclonal antibodies in an enzyme immunospot assay to detect isotype-specific antibody-secreting cells in pigs and chickens

Monoclonal antibodies directed against porcine immunoglobulin isotypes G, G1, G2, M, and A and against chicken immunoglobulin isotopes G, M, and A were tested in an antigen-specific spotforming cell (SFC) assay based on the principle of the enzyme immunoassay. The SFC assay was used to quantitate ovalbumin (OA)-specific antibody-secreting cells (ASC) in pigs that had been primed and boosted with OA. The SFC assay was also used to quantitate trinitrophenyl (TNP)-specific ASC in chickens that had been primed with TNP-conjugated keyhole lympet haemocyanin (TNP-KLH). Although, the classical plaque-forming cell (PFC) assay cannot reliably detect isotope-specific ASC in pigs and chickens, it can detect these cells in mice. Therefore, we compared the OA- and TNP-specific SFC assays with PFC assays that were specific for these antigens in mice. The study demonstrated that the SFC assay is superior to the PFC assay in detecting both OA-specific ASC and TNP-specific ASC. The frequencies of OA-specific and TNP-specific SFC detected in mice were of the same order of magnitude as those detected in pigs and chickens. We concluded that the SFC assay is the better method for quantitating ASC in pigs, chickens, and probably all domestic animals for which isotype-specific monoclonal antibodies are available.

The major histocompatibility complex and genetic control of antibody response to sheep red blood cells in chickens

The genetic association of the B-F/B-L region of the chicken major histocompatibility complex (MHC) with the antibody response to sheep red blood cells (SRBC) was investigated using three inbred lines of White Leghorn chickens. Two out of the three inbred lines of chickens. J1 and N1, were found to be a low responder to SRBC. Planned matings between the three inbred lines of chickens showed that the genetic regulation of the magnitude of the antibody response to SRBC was associated with the MHC. The low antibody response to SRBC was inherited as a recessive trait linked to the B15 MHC phenotype of the M1 inbred line.

Bone and cartilage formation in diffusion chambers by subcultured cells derived from the periosteum

Periosteal cells were enzymatically isolated from the tibiae of young chicks, introduced into cell culture, allowed to reach confluence, and subcultured. The freshly isolated or subcultured cells were loaded into diffusion chambers and implanted into the peritoneal cavity of athymic mice to test their osteo-chondrogenic potential in a contained in vivo location. Freshly isolated periosteal cells formed both bone and cartilage tissue in such test chambers, but with a relatively low incidence. In contrast, cultured periosteal cells consistently gave rise to bone and cartilage even after 10 population doublings. With further passages of cells, the osteo-chondrogenic potential diminished substantially, until complete loss of expressivity at 16 population doublings or longer. Cultured muscle fibroblasts, when loaded into diffusion chambers under identical conditions to those of cultured periosteal cells, formed neither bone nor cartilage. These observations suggest that periosteal cells of young chicks contain subsets of progenitor cells or mesenchymal stem cells which possess the potential to differentiate into osteoblasts or chondrocytes, and this potential is retained after enzymatic isolation and for several population doublings in culture.

B-G cDNA clones have multiple small repeats and hybridize to both chicken MHC regions.

We used rabbit antisera to the chicken MHC erythrocyte molecule B-G and to the class I alpha chain (B-F) to screen lambda gt11 cDNA expression libraries made with RNA selected by oligo-dT from bone marrow cells of anemic B19 homozygous chickens. Eight clones were found to encode B-G molecules which hybridize with sequences in the chicken MHC as defined by congenic strains; the fusion proteins react with multiple immune but not preimmune sera, they select antibodies from the antisera to B-G, which then react with distinct erythrocyte B-G protein patterns, and they elicit antibodies from mice which in turn react with authentic B-G proteins. None of the clones represent a complete message, some--if not all--bear introns, and none of them match with any sequences presently stored in the data banks. The following new information did, however, emerge. At least two homologous transcripts are present in this homozygous chicken, thereby formally proving the existence of an expressed multigene family. The 3' ends (3'UT) are simple sequences with 80% nucleotide identity between clones, while the 5' ends (either coding or noncoding) are composed of multiple short repeats which are far less similar. These repeats could explain the bewildering variation in size of B-G proteins within and between haplotypes. Southern blots of genomic chicken DNA gave complex patterns for most probes, with many bands in common using different probes, but few bands in common between haplotypes. The sequences detected are all present in the MHC, based on the congenic lines CB and CC. Most of these sequences map into the B-G region, but some map into the B-F/B-L region as defined by the haplotypes B15, B21, and their apparently reciprocal recombinants B21r3 and B15r1.

Distribution and function of non-lymphoid cells positive for monoclonal antibody CVI-ChNL-68.2 in healthy chickens and those infected with Marek's disease virus

Immuno-enzyme histochemistry was used to study the staining pattern and tissue distribution of monoclonal antibody CVI-ChNL-68.2 that specifically reacts with a subset of non-lymphoid cells in healthy chickens and those infected with Marek's disease virus (MDV). Functional characteristics of CVI-ChNL-68.2-positive cells, e.g. antigen uptake, are determined. In the liver CVI-ChNL-68.2 recognizes reticulum cells, whereas in the bursa of Fabricius it detects single cells in the interfollicular connective tissue. In the spleen CVI-ChNL-68.2 reacts selectively with the reticulum cells of the ellipsoid. In some MDV-infected chickens the splenic reticulum cells show a different staining and distribution pattern. Furthermore, the proliferative lesions associated with Marek's disease contain many CVI-ChNL-68.2-positive cells. The possible role of CVI-ChNL-68.2-positive cells in disseminating Marek's disease virus is discussed.

Renal and Adrenal Adenosine 3′,5′-Monophosphate Production and Corticosteroid Secretion in Response to Synthetic Chicken Parathyroid Hormone-(1–34)*

The activity of synthetic chicken (c) PTH-(1-34) amide was tested in dispersed chicken and rat kidney and adrenocortical cells. In the adrenal cells the effect of intact cPTH was also evaluated. In chicken kidney cells, the time- and dose-response patterns of cAMP production were similar for cPTH-(1-34) amide and human (h) PTH-(1-34), whereas rat kidney cells were considerably more sensitive to hPTH-(1-34) than to cPTH-(1-34) amide. The agonist effects of both hPTH-(1-34) and cPTH-(1-34) amide in kidney cells were inhibited by the bovine PTH-(3-34) analog. In chicken adrenocortical cells, cPTH-(1-34) amide stimulated cAMP production and steroid secretion. This action of the peptide was inhibited by bovine PTH-(3-34) and hPTH-(1-34), which by themselves showed no agonist effects. The maximal response of steroid secretion to cPTH-(1-34) amide was significantly lower than that to ACTH, but intact cPTH (supplied as a semipurified parathyroid extract) stimulated steriodogenesis to the same extent as ACTH. In rat adrenocortical cells, intact cPTH stimulated both cAMP formation and steriodogenesis, but cPTH-(1-34) amine showed no agonist effect. The action of the intact hormone in the rat adrenal could be inhibited by cPTH-(1-34) amide. The present results demonstrate the interaction of cPTH-(1-34) with kidney and adrenocortical cells of either chicken or rat. The cAMP and steroidogenic responses of the adrenocortical cells to PTH appear to be dependent (completely in the rat and partially in the chicken) on some sequence beyond the 1-34 region.

Calcium-dependent stimulation of estrogen secretion by FSH from theca cells of the domestic hen ( Gallus domesticus)

There is little information about the stimulation of estrogen secretion from theca cells of the domestic hen by follicle-stimulating hormone (FSH), and the mechanism of action of FSH through calcium has not been considered previously. The theca interna and externa cells from the third (F3) and fourth (F4) largest ovarian follicles of hens were separated, dispersed, and incubated in M199 with FSH (0.5 μg ml −1) or A23187 (0.1 or 1 μg ml −1) with or without ethylene glycol bis(β-aminoethyl ether) N, N′-tetraacetic acid (EGTA) (2 m M) in calcium-replete or in calcium-free M199. Alternatively, androstenedione (10 −6 M) was added to the cells as aromatizable substrate, with or without FSH and/or EGTA. Estradiol and estrone secreted into the media during a 4-hr incubation period were measured by RIA. FSH stimulated estradiol and estrone secretion from all the cell preparations. The effect of FSH was abolished by the addition of EGTA or in calcium-free medium. A23187 stimulated estradiol and estrone secretion by the same extent as FSH, but did not do so in calcium-free medium. Androstenedione enhanced estradiol and estrone secretion, but estrogen secretion was further raised by the simultaneous addition of FSH. This action of FSH on aromatization was also abolished by EGTA. This evidence supports the hypothesis that calcium, possibly of extracellular origin, is an important mediator in the stimulation of aromatase systems in thecal cells of chickens.

Immunoglobulin diversification in bursal duct-ligated chickens.

The role of external antigen contact on immunoglobulin (Ig) diversification occurring in chicken bursal cells was evaluated. The entry of environmental antigens into the lumen of the bursa of Fabricius was prevented by ligating the bursal duct prior to hatching (BDL: bursal duct ligation). We used two-dimensional gel electrophoresis to compare the heterogeneity of Ig molecules from bursa cells of normal and BDL chickens. We have found that Ig diversity obtained from BDL chickens' bursae in two-dimensional gel analysis was similar to that of control birds. Furthermore, by using two monoclonal anti-idiotype antibodies to study intrabursal Ig diversification we have shown that frequencies of the Cld-1 and Cld-2 idiotypes were also unaltered following bursal ligation. We conclude that primary B cell diversification in the bursa is independent of the external antigen flow from the bursal lumen.

Mutagenesis of the in-frame opal termination codon preceding nsP4 of Sindbis virus: studies of translational readthrough and its effect on virus replication

Sindbis virus (SIN) contains an in-frame opal termination codon in the nonstructural protein-coding region separating nsP3 and nsP4 and provides a useful tool to study the readthrough phenomenon of the termination codon in host cells and its role in viral replication. We have changed the opal codon by site-directed mutagenesis of a full-length SIN cDNA clone to either sense amino acids (serine, tryptophan, or arginine) or the other two translation termination codons (amber or ochre). Transcripts from all of the mutant cDNA clones were infectious when used to transfect chicken embryo fibroblasts. The resulting progeny virus stocks were then used to study the effects of these mutations on viral protein and RNA synthesis, growth properties, host range, and fitness compared with the parental strain. None of the mutants showed temperature sensitivity in plaquing efficiency or plaque morphology on chicken embryo fibroblast monolayers. Relative to the wild-type parent, the mutants containing sense replacements overproduced nsP34 but not nsP4 and made slightly decreased levels of nsP3, with a delay in its appearance. This indicates that the cleavage separating nsP3 and nsP4 occurs in these mutants and also that the level of nsP4 is not regulated solely by readthrough of the opal codon. The amber and ochre mutants produced decreased levels of nsP34, and the ochre mutant grew significantly more slowly than the other mutants or wild-type virus. For all five mutants, RNA synthesis early in infection was inhibited compared with that of the parental virus. This effect was apparent at multiplicities of infection of 20 PFU per cell but not at 100 PFU per cell. Using in situ hybridization to distinguish between mutant and wild-type plaques, we have studied the behavior of the serine mutant in a high-multiplicity growth competition experiment with wild-type virus. The wild-type virus eventually outcompeted the mutant after several passages, and these results indicate that this mutation has resulted in effects that are at least partially cis acting. Furthermore, by studying the growth, plaque formation, and protein synthesis of the mutants in various cell types, we have observed host range effects of the mutations, especially in mosquito and human cells. In addition, we have demonstrated, at least indirectly, that opal, amber, and ochre termination codons in the SIN nucleotide context can be suppressed in cultured cells of chicken, human, hamster, and mosquito origin.

Chicken Oocytes and Fibroblasts Express Different Apolipoproteins-B-Specific Receptors

We have previously characterized a 95-kDa plasma membrane receptor for low and very low density lipoproteins in chicken oocytes (George, R., Barber, D. L., and Schneider, W. J. (1987) J. Biol. Chem. 262, 16838-16847). We now report that somatic cells of chickens, such as fibroblasts, express a different receptor for these lipoproteins. This receptor has a Mr of 130,000 and is part of a regulatory system for cholesterol homeostasis analogous to the low density lipoprotein receptor pathway in mammalian cells. Oocytes produce only the 95-kDa receptor, while fibroblasts synthesize exclusively the 130-kDa receptor. In addition to their different Mr values, another distinctive feature of the two proteins was revealed by ligand blotting experiments: the oocyte receptor bound rabbit beta-VLDL (a class of apolipoprotein-B and -E containing lipoprotein particles), whereas the fibroblast receptor did not. Furthermore, polyclonal rabbit antibodies that recognize the oocyte 95-kDa receptor failed to cross-react with the 130-kDa protein on fibroblasts [corrected]. We suggest that different receptors have evolved in the chicken in order to facilitate the deposition of lipids into oocytes (i.e. yolk formation) with concomitant maintenance of cholesterol homeostasis in extraoocytic tissues.

A series expression for the surface area of an Ellipsoid and its application to the computation of the surface area of avian erythrocytes

Knowledge of the surface area of cells is necessary for biophysical studies in which the permeability coefficient of a cell-type for a solute is defined. Under the microscope, avian erythrocytes have the appearance of an oval discus usually with a central elongated nucleus. The dimensions of these cells have been obtained for a large range of species over the past century. However, estimates of the surface areas have been obtained using mathematically simplistic models such as flattened circular cylinders. We modelled red cells of the domestic chicken (Gallus domesticus) as ellipsoids using the previously published dimensions to obtain the three semi-axis lengths. Although the mathematical expression for the volume of an ellipsoid is well known, an expression for the surface area is not. We present a general expression for the surface area of an ellipsoid that is a power series involving elliptic integrals and functions; the latter being rapidly evaluated by computer using standard series expressions. Our estimates of area are compared with earlier ones and those obtained by numerical integration of the surface.

Innervation of the C cells of chicken ultimobranchial glands studied by immunohistochemistry, fluorescence microscopy, and electron microscopy.

Innervation of the ultimobranchial glands in the chicken was investigated by immunohistochemistry, fluorescence microscopy and electron microscopy. The nerve fibers distributed in ultimobranchial glands were clearly visualized by immunoperoxidase staining with antiserum to neurofilament triplet proteins (200K-, 150K- and 68K-dalton) extracted from chicken peripheral nerves. The ultimobranchial glands received numerous nerve fibers originating from both the recurrent laryngeal nerves and direct vagal branches. The left and right sides of the ultimobranchial region were asymmetrical. The left ultimobranchial gland had intimate contact with the vagus nerve trunk, especially with the distal vagal ganglion, but was somewhat separated from the recurrent nerve. The right gland touched the recurrent nerve, the medial edge being frequently penetrated by the nerve, but the gland was separated from the vagal trunk. The left gland was innervated mainly by the branches from the distal vagal ganglion, whereas the right gland received mostly the branches from the recurrent nerve. The carotid body was located cranially near to the ultimobranchial gland. Large nerve bundles in the ultimobranchial gland ran toward and entered into the carotid body. By fluorescence microscopy, nerve fibers in ultimobranchial glands were observed associated with blood vessels. Only a few fluorescent nerve fibers were present in close proximity to C cell groups; the C cells of ultimobranchial glands may receive very few adrenergic sympathetic fibers. By electron microscopy, numerous axons ensheathed with Schwann cell cytoplasm were in close contact with the surfaces of C cells. In addition, naked axons regarded as axon terminals or "en passant" synapses came into direct contact with C cells. The morphology of these axon terminals and synaptic endings suggest that ultimobranchial C cells of chickens are supplied mainly with cholinergic efferent type fibers. In the region where large nerve bundles and complex ramifications of nerve fibers were present, Schwann cell perikarya investing the axons were closely juxtaposed with C cells; long cytoplasmic processes of Schwann cells encompassed large portions of the cell surface. All of these features suggest that C-cell activity, i.e., secretion of hormones and catecholamines, may be regulated by nerve stimuli.

Presence of natural suppressor cells in the chicken embryo spleen and the effect of virus infection of the embryo on suppressor cell activity

Spleen cells but not the thymus or the bursa cells of chicken embryos suppressed the in vitro mitogenesis of spleen cells of adult syngeneic or allogeneic chickens. The natural suppressor cell activity of embryo spleen was present at embryonation day 16, reached peak levels at embryonation day 18 and disappeared at hatch. The embryo spleen cells did not by themselves respond to phytohemagglutinin stimulation in vitro. The suppressive effect of embryonic spleen cells on adult spleen cells was present when the embryonic cells were added at the time of or after initiation of the adult spleen mitogenic cultures. When the embryonic cells were added to the cultures of adult spleen cells after the blastogenic response of the adult cells had peaked, the embryonic cells inhibited the incorporation of the label into adult spleen cell blasts. The suppressive activity of the embryonic spleen cells was mediated by soluble suppressor product(s) secreted by these cells, and direct cell-to-cell contact between embryonic and adult spleen cells was not necessary for suppression to occur. Infection of embryos with turkey herpesvirus and Marek's disease virus reduced the suppressor cell activity of embryonic spleen, although substantial residual suppressor cell activity remained in virus-infected embryos. Several pathogenic or non-pathogenic isolates of infectious bursal disease virus did not appreciably alter the suppressor cell activity of embryonic spleen cells.