Synthesis, properties and thermal studies of oxorhenium(V) complexes with 3-hydrazino-5,6-diphenyl-1,2,4-triazine, benzimidazolethione and 2-hydrazinobenzimidazole. Mixed ligand complexes, pyrolytical products and biological activity.

A series of biologically active complexes of oxorhenium(V), were prepared by using the organic ligands 3-hydrazino-5,6-diphenyl-1,2,4-triazine (HL1), benzimidazolethione (H2L2) and 2-hydrazinobenzimidazole (H2L3). The mixed ligand complexes of oxorhenium(V) with the previous ligands and one of the following ligands: NH4SCN, 1,10-phenanthroline (1,10-phen), 8-hydroxyquinoline (8-OHquin) or glycine (Gly), were isolated. All the binary and mixed ligand complexes have monomeric structures and exist in the octahedral configuration. Thermal studies on these complexes showed the possibility of structural transformation from mononuclear into binuclear ones. The structures of all complexes and the corresponding thermal products were elucidated by elemental analyses, IR, electronic absorption and 1H NMR spectra, magnetic moments, conductance and TG-DSC measurements. The antifungal activities of the metal complexes towards Alternaria alternata and Aspergilus niger were tested and showed comparable behaviour with some well known antibiotics.

Effect of heat stress on production parameters and immune responses of commercial laying hens.

The present study was conducted to determine the adverse effects of high temperature and humidity not only on live performance and egg quality but also on immune function in commercial laying hens. One hundred eighty 31-wk-old laying hens at peak production were used in this study. Hens were housed in cages (15 cages of 4 birds/cage) in each of 3 environmental chambers and received 1 of 3 treatments. The 3 treatments were control (average temperature and relative humidity), cyclic (daily cyclic temperature and humidity), and heat stress (constant heat and humidity) for 5 wk. Different production and immune parameters were measured. Body weight and feed consumption were significantly reduced in hens in the heat stress group. Egg production, egg weight, shell weight, shell thickness, and specific gravity were significantly inhibited among hens in the heat stress group. Likewise, total white blood cell (WBC) counts and antibody production were significantly inhibited in hens in the heat stress group. In addition, mortality was higher in the heat stress group compared to the cyclic and control groups. Even though T- and B-lymphocyte activities were not significantly affected by any of the treatments, lymphocytes from hens in the heat stress group had the least activity at 1 wk following treatment. These results indicate that heat stress not only adversely affects production performance but also inhibits immune function.

Initiation of humoral immunity. I. The role of cytokines and hormones in the initiation of humoral immunity using T-independent and T-dependent antigens.

The early events during the initiation of immune responses following the injection of T-independent (lipopolysaccharide, LPS) and T-dependent (bovine serum albumin, BSA) antigens were studied in immature male chickens. Specifically, the role of cytokines and hormones in the initiation of humoral immunity against these antigens was investigated. Both interleukin-1 (IL-1) and tumor necrosis factor (TNF-alpha) increased significantly post-LPS but not post-BSA injection. While interleukin-2 (IL-2) significantly decreased post-LPS injection, IL-2 significantly increased post-BSA injection. Furthermore, corticosterone levels significantly increased and tri-iodothyronine (T(3)) levels significantly decreased post-LPS but not post-BSA injection. In this study, the results indicate that although LPS and BSA can induce a humoral antibody response in chickens, they activate different cytokines and neuroendocrine network systems.

Initiation of humoral immunity. II. The effects of T-independent and T-dependent antigens on the distribution of lymphocyte populations.

The effect of injecting T-independent (lipopolysaccharide, LPS) and T-dependent (bovine serum albumin, BSA) antigens on the redistribution of lymphocyte populations in immature male chickens was investigated. In the blood, percentages of total T-cells (CD3+), T-helper cells (CD4+), and T-cytotoxic/suppressor cells (CD8+) significantly decreased post-LPS injection (PLI) but not post-BSA injection (PBI), while percentages of monocytes/thrombocytes (K1+) significantly increased PLI. Interleukin-1 receptor expression on blood lymphocytes increased significantly PLI and PBI. In the spleen, the percentages of total T-cells (CD3+) increased significantly PLI and PBI, macrophage (K1+) percentages increased significantly PLI, while B-cell percentages decreased significantly PLI. These results indicate that following antigen injection, there is a redistribution of peripheral blood lymphocytes (specifically T-lymphocytes) to secondary lymphoid organs and the kinetics and magnitude of the changes can differ according to the type of antigen used.

Melatonin and the enhancement of immune responses in immature male chickens.

Understanding the role of melatonin in affecting different physiological functions, especially immune responses, is becoming increasingly important in the basic and applied sciences. Enhancing the immune response will result in increasing disease resistance and, therefore, improve production efficiency. The purpose of the present study was to investigate the effects of melatonin, administered during the light or dark period, on BW, feed consumption (FC), and immune responses of immature chickens. Eight-week-old Cornell White Leghorn males were used in this study. The doses of melatonin were 0, 5, 10, 20, and 40 mg/kg BW. Melatonin was administered s.c. every 24 h for 7 consecutive d. The chicks were randomly divided into two groups; one group received injection during the middle of the light period, and the other group received injection during the middle of the dark period. All birds received 16 h light and 8 h darkness during a 24-h period. Body weights were measured before and after melatonin treatment, and FC was also measured. After the seven injections, blood samples were collected from the brachial vein, and total white blood cell (WBC) counts, differential cell counts, and activities of T and B lymphocytes were measured. Body weight was not significantly affected by dose of melatonin or time of injection. Furthermore, melatonin did not significantly affect FC; however, FC was significantly lower in the group that was injected in the dark vs. light period. The WBC counts of birds injected with 40 mg melatonin/kg BW were significantly higher than the WBC counts of saline-injected birds. The heterophil/lymphocyte (H/L) ratios of birds injected during the light period were significantly higher than those of birds injected during the dark period. T- and B-lymphocyte proliferation were significantly higher in birds injected with 40 mg melatonin/kg BW compared to saline-injected birds. These results indicate that melatonin in vivo is important in enhancing not only circulating WBC but also activities of B and T lymphocytes of immature male chickens without adversely affecting BW.

Influence of genetic selection for antibody production against sheep blood cells on energy metabolism in laying hens.

Genetic selection in chickens has been utilized to enhance immune responses that may influence resistance to diseases. It is important, however, to investigate the effects of this selection on other physiological processes. Therefore, this study was conducted to determine whether selection for antibody (Ab) production against SRBC has an effect on energy metabolism. Laying hens from three lines were used in this study, two of which were selected for 15 generations for Ab response against SRBC, and the third was nonselected and randombred. The hens used were from four different groups. The first two groups were from the lines that were selected for either high (SH) or low (SL) Ab production. The second two groups were control birds (nonselected) that had either high (CH) or low (CL) Ab titers that were similar to those in the SH and SL lines, respectively. The birds were housed in climate-respiration chambers. Body weights and energy metabolism were measured. Body weights of SL hens were significantly (P < 0.05) higher than those of SH hens. However, the BW for the two nonselected groups were similar but significantly less than the SL group. Energy partitioning was similar in all groups; however, ME for maintenance for the selected groups (119 kcal x kg(-0.75 x d(-1)) was numerically, but not significantly (P < 0.09), higher than that of the nonselected groups (112 kcal x kg(-0.75) x d(-1)). These results suggest that divergent selection for Ab may result in an increase in the requirements of energy for maintenance, which is not directly related to the amount of Ab produced. Furthermore, these results support previous findings of the presence of a negative correlation between BW and the levels of Ab in selected lines.

Effects of photoperiod and melatonin on lymphocyte activities in male broiler chickens.

Understanding the role of the pineal gland in regulating the immune response and the role of photoperiod in influencing pineal gland secretions are becoming increasingly important. The purposes of the present experiments were to investigate the effects of different photoperiod regimens on T- and B-lymphocyte activities in broiler chickens. Next, the influence of different photoperiod regimens on the responsiveness of lymphocytes to melatonin in vitro was examined. The effect of melatonin in vitro on lymphocyte activities was also studied, regardless of the photoperiod received. Finally, the effects of photoperiod on the profiles of different splenocyte cell types were investigated. To study the effect of photoperiod on lymphocyte activities, different photoperiod regimens were used. These were: constant lighting, 23 h light:1 h darkness; intermediate lighting, 12 h light:12 h darkness; and intermittent lighting, 1 h light:3 h darkness. Peripheral blood and splenic lymphocyte activities were tested at 3 and 6 wk of age by performing a mitogen cell-proliferation assay with a polyclonal T-cell mitogen, concanavalin A (Con A), and T-dependent B-cell mitogen, pokeweed mitogen (PWM). To study the effect of photoperiod on the responsiveness of lymphocytes to melatonin in vitro or the effect of melatonin in vitro on lymphocyte activities regardless of photoperiod received, lymphocytes from the chickens that were exposed to the different photoperiod regimens were incubated with mitogen and different concentrations of melatonin. To study the effect of photoperiod on profiles of different cell types, the percentages of splenocyte subpopulations from birds exposed to different photo-periods were determined using flow cytometry with CD4+, CD8+, CD3+, and B-cell markers. The results of these studies indicate that splenic T and B lymphocytes from 6-wk-old chickens grown in intermittent lighting had higher activities than those from chickens grown in constant lighting. Peripheral blood and splenic lymphocytes from chickens raised under constant lighting were more responsive to melatonin in vitro than those from chickens raised under intermittent lighting. This difference in response may be due to lower levels of melatonin in birds receiving constant lighting, making them more sensitive to melatonin in vitro. Melatonin in vitro enhanced the mitogenic response of peripheral blood T lymphocytes from 6-wk-old chickens, splenic T lymphocytes from 3-wk-old chickens, and splenic T and possibly B lymphocytes from 6-wk-old chickens. Finally, intermittent lighting increased the percentages of splenic CD4+, CD8+, and CD3+ cells but not B-cell subpopulations at 6 wk of age, presumably because of increased levels of melatonin in birds receiving intermittent lighting. Our results re-emphasize the importance of melatonin in regulating host immune response; this regulation could be accomplished through exposing broiler chicks to intermittent lighting.

Effect of genetic selection and MHC haplotypes on lymphocyte proliferation and interleukin-2 like activity in chicken lines selected for high and low antibody production against sheep red blood cells.

Chickens from third generation matings of lines of chickens selected for high (HA) and low (LA) antibody production to sheep red blood cells (SRBC) and typed for MHC genotypes B13/13, B13/21, and B21/21 were used in this study. Chickens from both lines carried all the three genotypes B13/13, B13/21, and B21/21. To study T- and B-lymphocytes mitogenic activity, 12-week-old female chickens were injected intravenously with 0.2 ml of 9% SRBC and spleens were collected at 0, 6 h, and 6 day post-antigen injection (pAg). Isolated lymphocytes were incubated with either Concanavalin-A (Con-A) for T-cell activity, or Pokeweed mitogen (PWM) for B-cell activity and thymidine 3H uptakes were measured. To study the Interleukin-2 (IL-2)-like activity in the same lines and genotypes, splenic lymphocytes from 12-week-old chickens were passed through nylon wool columns to enrich the T-cell population. After a 24 h incubation with Con-A, the conditioned media (CM) were collected. The CM were tested for IL-2 like activity by determining whether they altered the proliferation of Con-A stimulated T cells. This proliferation effect was then compared to that of a reference conditioned media (RCM) prepared from K-strain birds and that were used as the standard for the assay. There was no significant difference (p > 0.05) in IL-2 like activity between HA and LA lines, however, the LA was significantly higher than HA (p < 0.05) in T- and B-cell mitogenic activity. The genotype B13/13 had significantly higher (p < 0.05) IL-2 like activity than the B21/21. The genotype B13/13 was also significantly higher (p < 0.05) in T- and B-cell mitogenic activity than the B21/21. At 0 h, pAg T- and B-mitogenic activity was significantly higher (p < 0.05) than 6 h. In summary, our results indicate that although the birds were selected for high antibody production to SRBC, their lymphocyte mitogenic activity was lower than those selected for low antibody production. Hence, humoral and cell-mediated immune responses appear to be under different genetic controls, and that selection for greater humoral response may be at the expense of cellular responses. Our results also suggest differences in IL-2 like activity production between chickens carrying different MHC B-haplotypes, and that genetic control of such activity is possibly linked to the MHC genes.

Effect of induced molting in laying hens on production and immune parameters.

A total of 600 commercial strain (DeKalb) Single Comb White Leghorn hens, 80 wk of age, were used in this study to determine the effects of different induced molting programs on production and immune parameters. The hens were randomly divided into four treatment groups (three experimental and one control) of 150 hens each. The hens in the first treatment group were fed a layer ration containing 20,000 ppm of zinc for 5 d, and received a reduced photoperiod of 8 h/d for 5 d (Zn group). In the second group, feed was withdrawn for 10 d, the photoperiod was reduced to 8 h/d and oyster shell and water were provided for ad libitum consumption. At Day 11, hens consumed corn and oyster shell ad libitum until Day 30 and at Day 31, hens were returned to a full feed layer ration and received 16 h of light/d [California treatment (CAL group)]. In the third treatment, light was reduced to 8 h/d, and oyster shell was provided for ad libitum consumption until Day 60. Feed and water were removed for the first 2 d and on Days 4, 6, and 8. On Days 3, 5, 7, and 9, hens were fed 45 g of feed per hen. On Day 10 until Day 60, hens were fed 90 g/hen and at Day 61, hens were returned to the layer ration ad libitum and received 16 h of light/d [on-again, off-again program (ON-OFF group)]. The last group served as controls (CONT). Body weight, egg production, egg size, internal egg quality, shell weight, and mortality were determined. Total circulating leukocytes, differential leukocyte counts, and antibody production were also measured. The results demonstrated that induced molting significantly increased egg production from 64% to 77 to 83%, Haugh units from 80.4 to 85.9 to 87.3, and shell weight from 5.3 g to 6.3 to 6.4 g when compared to CONT. The body weight of the molted hens decreased significantly to 84.8, 74.5, and 88% of the initial body weight for Zn, CAL, and ON-OFF groups, respectively. The total circulating leukocytes was significantly lower in molted hens than in CONT hens. Differential leukocyte counts were affected by all induced molting programs and the heterophil to lymphocyte ratio was significantly increased, reaching 0.61, whereas that of CONT was only 0.20. Antibody production was largely unaffected by any of the induced molting programs.

Effect of melatonin and lighting schedule on energy metabolism in broiler chickens.

The effect of melatonin and lighting schedule on energy metabolism in broiler chickens was studied. Eight groups of six female broiler chickens each were assigned to a continuous lighting schedule [23 h light (L):1 h darkness (D)] or an intermittent lighting schedule (1L:3D), and were fed a diet with or without melatonin (40 ppm). At 21 d of age, the chickens were placed in respiration chambers for 20 d. Energy and nitrogen balances, heat production, and physical activity were measured per group. The only effect of melatonin on energy metabolism, was a decreasing effect on activity-related heat production. The intermittent lighting schedule induced improved feed conversion, higher metabolizability of the diet, and lower physical activity compared to continuous lighting. No interactions between melatonin and lighting schedule were found on energy metabolism traits. Lighting schedule strongly affected daily heat production pattern (total, activity-related, and nonactivity-related heat production). Melatonin had a reducing effect on activity-related heat production during the day, especially during light periods. The present study demonstrated that reduced energy expenditure for physical activity, caused by the supplementation of melatonin to the diet, might be a reason for the often observed improvement of feed conversion. Furthermore, this study showed that feed conversion was improved with an intermittent lighting schedule, which was related to higher metabolizability and lower energy expenditure on physical activity, compared to continuous lighting.

The role of neuroendocrine immune interactions in the initiation of humoral immunity in chickens.

The presence of neuroendocrine immune interaction in mammalian species has been studied extensively and has been established. However, such an interaction is not as well established in avian species. Furthermore, the role of such an interaction in the initiation of humoral immunity is not well understood. Therefore, the present studies were conducted to determine mechanisms involved in the initiation of humoral immunity in chickens. Cornell K-strain White Leghorn immature male chickens were used for all the experiments. Changes in hormonal and leukocyte profiles after antigen stimulation were studied. The ability of different leukocytes to produce ACTH was also investigated. It was concluded that the first step in the initiation of humoral immunity after antigen exposure is the release of interleukin-1 by macrophages, which in turn stimulates the production of CRF by hypothalamus and/or leukocytes. It is important to mention that CRF production could also be a direct effect of antigen stimulation. The CRF will then stimulate ACTH production by anterior pituitary and/or leukocytes. In addition, CRF will directly enhance lymphocyte activities in the spleen. Corticosteroid production will be stimulated by ACTH and will cause redistribution of lymphocytes from circulation to secondary lymphoid organs such as the spleen for antigen processing and eventual production of antibodies against the invading antigens. Finally, both ACTH and corticosteroids will later act in a negative feedback manner to regulate and control the process of antibody production by inhibiting lymphocyte activities and/or reducing the responsiveness to different stimuli.

Effects of corticotropin releasing factor on the production of adrenocorticotropic hormone by leukocyte populations.

1. Corticotropin-releasing factor (CRF), a neuropeptide with immunomodulating properties, is known to stimulate avian splenic leukocytes to produce adrenocorticotropic hormone (ACTH). 2. The present study was to determine which avian splenic leukocyte subpopulation(s) produce ACTH in response to CRF stimulation. 3. Splenic leukocytes from 8-week-old male chickens were isolated on Histopaque 1077 and macrophages were separated from lymphocytes by adherence to a polystyrene surface. 4. Different concentrations of CRF (0, 5, 50, 500 or 1000 ng/m) were incubated with the different leukocyte populations, supernatants were collected and ACTH was measured using a radioimmunoassay. 5. Isolated macrophages, stimulated with CRF, produced significantly more ACTH than either unstimulated macrophages or CRF-stimulated lymphocytes, suggesting that ACTH may be produced by a particular subset of leukocytes, the macrophages (and monocytes), in response to CRF stimulation.

Synthesis of novel heterocycles through reaction of indolin-2-one derivatives with active methylene and amino reagents.

Several new spiro compounds were synthesized via one-pot ternary condensation of isatin, malononitrile and each of thiobarbituric acid, barbituric acid, 3-methyl-pyrazolin-5-one, 1-phenyl-3-methyl-pyrazolin-5-one, acetylacetone, benzoylacetone, ethyl acetoacetate, phenacyl cyanide or ethyl-cyanoacetate dimer. Structures and reaction mechanism were reported and supported via a second synthetic route.

Changes in blood and spleen lymphocyte populations following antigen challenge in immature male chickens.

1. The effects of antigen (Ag) injection on the distribution of lymphocyte populations of Cornell K-strain male chickens were studied. 2. Two experiments were conducted. In the first, chickens were injected with Brucella abortus (BA), a purported T-independent antigen. In the second, chickens were injected with sheep red blood cells (SRBC), a T-dependent antigen. Peripheral blood lymphocytes (PBL) and spleen lymphocytes isolated at 0, 3, 6, 9, 12 and 24 h following Ag injection were stained with monoclonal antibodies (mAb) detecting B-lymphocytes, CD4+ and CD8+ cells. 3. B-lymphocytes in the blood or spleen showed no significant changes following either BA or SRBC injection. In contrast, CD4+ cells were decreased in the blood and increased in the spleen following BA and SRBC injections. CD8+ cells were decreased in both blood and spleen following BA injection but were unchanged in either blood or the spleen following SRBC injection. 4. These results indicate that there is a change in both spleen and circulating lymphocyte populations, especially T-helper cells, following Ag injection. T-helper cells are apparently the primary population involved in the initiation of humoral immunity.

Synthesis and antibacterial testing of some new quinolines, pyridazinoquinolines and spiroindoloquinolines.

3-Dicyanomethylideneindole derivatives were involved in (i) ring expansion reactions in alcoholic piperidine to form new quinolines from which a new pyridazinoquinoline was synthesised; and (ii) formation of new spiroindoloquinolines by reactions with cyclohexanone and beta-tetralone. The suggested structures of the new products were confirmed by IR, 1H-NMR, 13C-NMR and mass spectral analyses. Some of the new derivatives were active against the bacteria Escherichia cell.

Effects of in vitro corticosterone on chicken T- and B-lymphocyte proliferation.

1. The effects of corticosterone and the time of its addition to cultures, on concanavalin A (Con-A) and pokeweed mitogen (PWM)-induced lymphocyte proliferation were studied. 2. Peripheral blood lymphocytes (PBL) were isolated from Cornell K-strain Single Comb White Leghorn immature male chickens and cultured with various concentrations of Con-A or PWM. Corticosterone, in different concentrations, was added to the cultures either 2 h before or 2 h after the addition of the respective mitogen. 3. Addition of corticosterone 2 h before the mitogens caused a significant suppression of lymphocyte proliferation in response to both Con-A and PWM stimulation. Also addition of corticosterone 2 h after the mitogens caused significant suppression of proliferation in response to both mitogens; however, the degree of suppression was not as great. 4. The results indicate that after early activation events are initiated by the mitogens, lymphocytes are less sensitive to the effects of corticosterone. Because less suppression was seen in the cultures preincubated with PWM than those with Con-A, it is likely that there are different sensitivities to corticosterone in the cell populations that respond to these mitogens.

Effects of corticosterone in vivo and in vitro on adrenocorticotropic hormone production by corticotropin releasing factor-stimulated leukocytes.

Corticotropin releasing factor (CRF) and corticosterone have been shown to affect immune cell function. Previously, we have shown that CRF stimulates immunoreactive adrenocorticotropic hormone (ACTH) production by leukocytes. In this study, splenic leukocytes from corticosterone-injected chickens failed to show a CRF-induced increase in ACTH production. In addition, corticosterone in vitro inhibited the production of leukocyte ACTH as well as the stimulatory effect of CRF on splenic leukocyte ACTH production. These findings show that, as with anterior pituitary ACTH production, CRF-stimulated leukocyte ACTH production is inhibited by glucocorticoids.

Validation of an assay to measure adrenocorticotropin in plasma and from chicken leukocytes.

A RIA for mammalian adrenocorticotropic hormone (ACTH) was modified and validated to measure chicken ACTH. The assay was capable of detecting an increase in chicken plasma ACTH following treatments known to increase plasma ACTH. Both splenic and peripheral blood leukocytes stimulated with corticotropin-releasing factor (CRF) showed a significant increase in ACTH production compared with unstimulated leukocytes. This finding supports the conclusion that the substance produced by leukocytes previously shown in our laboratory to stimulate adrenal cells to secrete corticosterone is immunoreactive ACTH.

Inhibition of adrenal steroidogenesis, neonatal feed restriction, and pituitary-adrenal axis response to subsequent fasting in chickens.

White Plymouth Rock chickens placed under 60% feed restriction or ad libitum feeding, with or without metyrapone (adrenal blocking agent) treatment, from 4 to 6 days of age were subjected to either 8 or 24 hr feed deprivation at 36 days of age. Chicks subjected to the neonatal 60% feed restriction (60R) but not those provided metyrapone during the procedure (60M) had elevated heterophil/lymphocyte (H/L) ratios. However, there was no difference in plasma corticosterone and ACTH responses between 60R and 60M chicks. Except for increases in H/L and plasma corticosterone concentrations among ad libitum fed (AL) and 60M chickens, respectively, there was no indication of stress response attributable to the subsequent 8 hr fast. Feed withdrawal for 24 h did not cause rises in H/L ratios and plasma levels of corticosterone of chicks that had been subjected to early 60% feed restriction with nonmetyrapone-treated feed. In contrast, chicks of other regimens had elevated H/L and plasma corticosterone responses when exposed to a similar procedure. Except for those fed ad libitum during the neonatal stage, circulating levels of ACTH declined following the 24-hr fast. These results demonstrate that stress early in life without concurrent rises in circulating corticosteroid levels may not help the biological system in coping with subsequent stressors.

The effects of adrenocorticotropic hormone and heat stress on the distribution of lymphocyte populations in immature male chickens.

This study investigated the effects of heat stress and adrenocorticotropic hormone (ACTH) on the distribution of lymphocyte populations. Two experiments were conducted; each used 12-wk-old Cornell K-strain male chickens. In Experiment 1, birds were exposed to a temperature of 35 C, 6 h/d for 5 d and control birds were maintained at 24 C. In Experiment 2, birds received daily i.m. injections of 50 IU/kg body weight of ACTH for 5 d and control birds received .9% saline. On Day 6, blood and spleens were collected and lymphocytes were isolated. Indirect immunofluorescent labeling of lymphocytes were performed to detect B lymphocytes, CD4+ cells, and CD8+ cells. Neither ACTH injection nor heat stress affected percentages of B lymphocytes in the blood or the spleen. The CD4+ cells decreased significantly in the blood of ACTH-injected and heat-stressed birds and significantly increased in the spleens of heat-stressed birds. The CD4+ cells in the spleens of ACTH-injected birds did not differ from controls. The CD8+ cells significantly declined in the blood following both ACTH injection and heat stress and significantly increased in the spleen of the ACTH-injected birds but did not differ from controls in the heat-stressed birds. These results indicate that stress factors lead to redistribution of different lymphocyte populations.