Production and persistence of antibodies in chickens to sheep erythrocytes. 2. Resistance to infectious diseases

Impact of genetics on disease resistance

The genetics of a bird or flock has a profound impact on its ability to resist disease, because genetics define the maximum achievable performance level. Careful attention should be paid to genetics as an important component of a comprehensive disease management program including high-level biosecurity, sanitation, and appropriate vaccination programs. Some specific genes (e.g., the MHC) are known to play a role in disease resistance, but resistance is generally a polygenic phenomenon. Future research directions will expand knowledge of the impact of genetics on disease resistance by identifying non-MHC genetic control of resistance and by further elucidating mechanisms regulating expression of genes related to immune response.

Mode of inheritance of unselected traits in lines of chickens selected for high or low antibody response to sheep red blood cells. 1. Resistance to marble spleen disease virus and juvenile body weight

Two lines of White Leghorns that had undergone long-term selection for high (HH) or low (LL) antibody response to sheep red blood cell antigen(s) formed the nuclear lines for this experiment. Matings were made in a full diallel cross to produce in a single hatch from age-contemporary breeders the parental lines, reciprocal F1 and F2 crosses, and backcrosses for 16 progeny types. For males and females, there were parental line differences in BW to 42 d of age, after which there was decline between lines for males. Differences in BW between reciprocal F1 crosses and maternal heterosis declined with age, primarily reflecting dissipation of effects of egg weight. Heterosis of BW was dependent on the particular F1 cross and recombination effects were not important. At 50 d of age chicks were inoculated with either a 1 or 10% suspension of spleen extract from chickens infected with marble spleen disease virus (MSDV). A third group served as uninjected controls. Response to MSDV was evaluated by spleen weight 6 d after inoculation. Spleen weights relative to BW of control chicks were heavier for the HH than LL line with evidence from the crosses of sexlinkage and negative heterosis. Line LL chicks were more resistant to MSDV than Line HH chicks was F1 crosses intermediate to and different from either parental line with no evidence of heterosis.

Mode of inheritance of unselected traits in lines of chickens selected for high or low antibody response to sheep red blood cells. 2. Heterophils, lymphocytes, and hematocrits

The nuclear lines for this experiment were White Leghorns that had undergone long-term selection for high (HH) or low (LL) antibody response to sheep red blood cell antigen(s). Sixteen progeny types consisting of parental lines, reciprocal F1 and F2 crosses, and backcrosses were produced in a single hatch from age-contemporary parents. At 30 d of age, blood was obtained from a random sample of 10 males per progeny type (n = 160) and slides prepared for subsequent determination of number of heterophils and lymphocytes. Twelve days later, blood was collected from random samples of 10 males and 10 females per progeny type (n = 320) for measuring hematocrits. There were no differences between parental lines for heterophils, lymphocytes, or the heterophil:lymphocyte ratio. Reciprocal effects were evident in the F1 crosses and directional heterosis was present in one cross but not the other. Neither maternal heterosis nor recombination effects were significant for either heterophils or lymphocytes. Although hematocrits were similar for males and females and parental lines, sex-linked and recombination effects appeared to be important.

Alternative hypotheses linking the immune system and mate choice for good genes

Why do males often have extravagant morphological and behavioural traits, and why do females prefer to mate with such males? The answers have been the focus of considerable debate since Darwin's The descent of man, and selection in relation to sex appeared in 1871. Recently the broadening of investigation to include fields outside evolutionary biology has shed new light on mate choice and sexual selection. Here, we focus on a specific set of hypotheses relating the biology of resisting disease-causing organisms with the production of condition-dependent sexual signals (advertisements). We present a framework that distinguishes three different hypotheses about trade-offs within the immune system that affect general condition. Hamilton and Zuk's original hypothesis suggests that hosts fight off disease through resistance to particular pathogens, which consequently lowers resistance to other pathogens. Changes in pathogens over evolutionary time in turn favours changes in which genes confer the best resistance. Alternatively, the immunocompetence hypotheses suggests that the energetic costs of mounting a response to any pathogen compete for resources with other things, such as producing or maintaining advertisements. Finally, improving resistance to pathogens could increase the negative impacts of the immune system on the host, via immunopathologies such as allergies or autoimmune diseases. If both disease and immunopathology affect condition, then sexual advertisements could signal a balance between the two. Studies of hypothesized links between genes, condition, the immune system and advertisements likely will require careful consideration of which hypothesis is being considered, and may necessitate different measures of immune system responses and different experimental protocols.

The effect of stress on the response of chickens to coccidiosis vaccination

Six-week-old Leghorn chickens, which had been adapted to both their environment and cage mates, were orally inoculated with 400 Eimeria tenella oocysts as a means of low-dose vaccination. At 2, 3, 4, 5 or 6 days after vaccine administration, the birds were subject to 24 h of social stress through a prescribed method of random redistribution. Two weeks after vaccine administration, the birds were challenged by oral inoculation with 8000 oocysts. Caecal lesion scores were determined 6 days after challenge. Vaccinated chickens were more resistant to lesion formation than unvaccinated controls, and protection, as determined by lower lesion scores, was significantly enhanced when stress in the form of social disruption was applied on the fourth day following vaccine administration.

Variation in toe-web response of turkey poults to phytohemagglutinin-P and their resistance to Escherichia coli challenge

One thousand 5-wk-old male turkeys from each of two commercial strains (A and B) were grouped into low, medium, and high responders based on the cutaneous basophil hypersensitivity (CBH) response obtained 24 h after toe-web inoculation with 100 micrograms of phytohemagglutinin-P (PHA-P). The CBH response for Strain A was higher than strain B (P = 0.00001) and ranged from 0 to 1.95 mm, with a mean of 0.66, whereas the CBH response for Strain B ranged from 0 to 1.67 mm with a mean of 0.38. At 6 wk of age, 36 birds from each of the six response groups were inoculated into the left thoracic air sac with 1.5 x 10(7) cfu of an early log phase broth culture of Escherichia coli. Samples of 5 or 10 birds were necropsied from each of the six groups at 7, 14, 28, and 42 d postinfection (PI). Birds were scored for air-sacculitis/pericarditis (AS) and turkey osteomyelitis complex (TOC). Overall mortality of birds inoculated with E. coli was 31%. There were no mortalities in unchallenged controls. Strain A had significantly higher Week 1 mortality, marginally higher overall mortality (P = 0.1), and higher AS scores than Strain B. There were no TOC lesions detected until 7 d PI, after which all mortalities had TOC lesions in multiple sites. The differences in CBH response within each strain were not clearly correlated to E. coli susceptibility. However, these data suggest that air sac inoculation of E. coli can provide a useful model for the study of TOC. The greater incidence of disease in Strain A indicates that an enhanced inflammatory response may increase susceptibility to E. coli septicemia.

Effect of tumor necrosis factor-alpha on progesterone production by granulosa cells in laying hens of different genetic lines

In vitro progesterone production by granulosa cells in the presence or absence of human recombinant tumor necrosis factor-alpha (hrTNF-alpha) was measured at 10, 20, and 30 wk of egg production in White Leghorn hens selected for high (HA)- or low-antibody (LA) response to sheep red blood cell challenge. Isolated granulosa cells from the three largest preovulatory follicles (F1-F3) were incubated with 5 or 250 ng/ml hrTNF-alpha, and progesterone production was determined by the use of a validated radioimmunoassay. F1, F2 and F3 granulosa cells from HA hens produced more (P < or = 0.05) progesterone (140.8, 107.2, and 49.7 ng/ml) than LA hens (109.4, 78.9, and 26.9 ng/ml). The treatment of granulosa cells with hrTNF-alpha consistently inhibited (P < or = 0.05) progesterone secretion by all follicles among HA and LA hens, but not always at both doses. Generally, 5 ng/ml hrTNF-alpha was the maximum inhibitory dose. In the laying hen, a decrease in steroid production in response to cytokines may upset the steroid balance created by follicular hierarchy and inhibit or delay ovulation.

Genetic studies on primary antibody response to sheep erythrocytes in guinea fowl

1. The primary antibody response to sheep erythrocytes was determined by haemagglutination test in guinea fowl. The effects of various genetic and non-genetic factors on immune response to sheep RBCs in guinea fowl were also estimated. 2. The immune response to sheep RBCs was normally distributed in guinea fowl with mean titre at 1.534 +/- 0.014. 3. In guinea fowl, effects on titre values of sire and variety (feather colour) were significant whereas sex and sex x variety interaction effects were non-significant. 4. The estimate of heritability for immune response to sheep RBCs in guinea fowl was 0.35 +/- 0.17.

Immune and physiological responses of turkeys with green-liver osteomyelitis complex

A study of field turkeys was undertaken in order to determine the involvement of relative immunological differences in the etiology of turkey osteomyelitis complex (TOC). Lame and normal turkeys were sampled from commercial flocks just prior to processing in two separate trials. After testing for functions of both humoral and cellular immunity, the turkeys were necropsied and examined for lesions of TOC. There were significantly higher relative spleen and over weights and significantly lower body weights and relative bursal weights in birds with TOC. The birds with TOC had lower response to phytohemagglutinin-P in both in vivo and in vitro tests as well as lower circulating lymphocyte counts and higher monocyte, heterophil, and total white blood cell counts. There was a significantly higher antibody response to sheep red blood cells in turkeys with TOC, whereas antibody response to Salmonella pullorum antigen was not different. There were no significant differences in the percentages of mononuclear cells or heterophils able to phagocytize bacteria or latex particles, or kill bacteria; however, the heterophils from turkeys with TOC lesions did phagocytize significantly fewer latex particles per cell than did those of the healthy turkeys. Total serum protein, uric acid, and blood urea nitrogen levels were higher in birds with TOC, whereas hemoglobin, iron, alkaline phosphatase, and gamma-glutamyl-transferase levels were lower. Although many of the differences in birds with TOC could be caused by the normal host reaction to infection, further study may reveal innate differences that contribute to susceptibility to TOC.

Immunocompetence, ornamentation, and viability of male barn swallows (Hirundo rustica)

Immunocompetence (i.e., the ability to produce an immune response to pathogens) can be predicted to influence the chances that organisms have to survive and reproduce. In this study we simulated a challenge to the immune systems of male barn swallows (Hirundo rustica) by injecting them intraperitoneally with a multigenic antigen, sheep red blood cells, and we analyzed long-term survival in relation to their immunocompetence. Males were assigned to four groups that differed for the treatment of the length of the outermost tail feathers, a sexually dimorphic ornamental character that is currently under directional sexual selection. Immunocompetence was measured as change of concentration of gamma globulins relative to plasma proteins. The intensity of the immune response was independent of age. Males that showed the highest short-term response to sheep red blood cells were more likely to survive until the breeding season following that in which they had been inoculated, a pattern consistently observed within each experimental group. Males with comparatively long tails were more likely to survive than those with short tails. To our knowledge, the results of this study are the first to demonstrate that immunocompetence can predict long-term survival in a free-ranging vertebrate. Moreover, they are compatible with current models of parasite-mediated sexual selection because long-tailed males are more immunocompetent than short-tailed ones, and females, by preferring to mate with the most ornamented males, may acquire the "good genes" for high immunocompetence and, hence, for high viability of their offspring.

Group selection for adaptation to multiple-hen cages: humoral immune response

A selected line of White Leghorns, which has shown improved survivability and reduced feather loss in large multiple-hen cages, was evaluated for humoral immune response to SRBC under both stressed and unstressed conditions. Three lines of chickens (selected, control, and commercial) were housed in either single- (1 hen) or multiple-hen cages (12 hens, social competition) and subjected to a cold ambient temperature (0 C) at 33 wk of age and to two heating episodes (38 C) at 44 wk of age. Each hen was challenged intravenously with 1 mL of a 7% saline suspension of SRBC at the time that cold exposure was initiated. Hens subjected to high ambient temperatures had been exposed previously to a cold temperature, but were not challenged with SRBC until 16 to 18 h following the end of the second heating episode. Exposure to cold caused immunosuppression in single-caged hens, but not in hens in colony cages. Single- vs colony-caged hens of the control environment challenged with SRBC at 33 wk of age had similar primary hemagglutinin responses to SRBC. Hens subjected to heat experienced immunosuppression at 9 and 12 d following challenge to SRBC when compared to the controls. Hens of multiple-bird cages challenged with antigen at 44 wk of age had a significantly lower hemagglutinin response to SRBC than those reared in single-bird cages. The three lines of genetic stock had similar primary hemagglutinin responses to SRBC; the interactions of genetic stock with cage size or environmental temperature were not significant. It was concluded that genetically selecting hens for survival in multiple-hen cages did not affect their humoral immune response to SRBC.

Genetic differences and heritability of antibody response to Escherichia coli vaccination in young broiler chicks

Broiler chicken lines, selected divergently for high (HC) or low (LC) antibody titer to Escherichia coli vaccination at an early age, were evaluated for antibody response at the S5 and S9 generations of selection. The full-pedigreed populations consisted of about 300 and 400 chicks per line in S5 and S9, respectively. At S5, all chicks were vaccinated at 10 d of age (VA10) and antibody titer was determined twice for each chick, at 8 and 12 d postvaccination (dPV). At S9, each line was divided into two equal groups; in the HC line, one group was vaccinated at 8 d of age (VA8), and the other at 10 d of age (VA10), whereas in the LC line, one group was VA10 and the other was VA12. Antibody titers were determined twice for each chick, 8 and 10 dPV. The effects of line, age at vaccination (VA), and days for antibody development (dPV) were tested, and the heritability of antibody titer was estimated for each line-VA-dPV set of data. The HC and LC lines differed significantly in the maturation process of their immune systems. The percentage of chicks with detectable antibody at 18 d of age (VA10-8 dPV) among HC chicks was significantly higher than among LC chicks (85 vs 48% in S5 and 96 vs 63% in S9). In S9, 90% of the HC chicks had already responded at 16 d of age and 100% at 18 d of age, whereas among the LC chicks, only 62% were positive at 18 d of age, increasing to no more than 98% at 22 d of age. The results demonstrates that selection of antibody titer to E. coli vaccination at 20 d of age actually affects the earliest age of immune response, as the immune system of the HC chicks matures earlier than that of the LC chicks. The HC S9 chicks at 8 dPV exhibited a fourfold higher antibody titer than their LC 8 counterparts. This difference further increased at 10 dPV, indicating that the lines differed not only in the level of antibody at a specific age, but also in their rate of antibody titer development. The highest estimate of heritability was very similar in both lines (0.44 and 0.42 in HC and LC, respectively). However, in the HC line this heritability was exhibited at 18 d of age, and only at 22 d in the LC line. Thus, both lines have a similar amount of genetic variation for early immune response, but in the HC line this variation is fully expressed 4 d earlier than in the LC line. These results suggest that selection for high or low antibody response in young chicks results in early or late antibody production, respectively. To maximize the efficiency of selection for early immune response, one must determine the best vaccination age and timing of antibody evaluation in any given population, and these values must be revalidated and updated as selection proceeds.

Differences in distribution of lymphocyte antigens in chicken lines divergently selected for antibody responses to sheep red blood cells

The proportion of cells showing differentiation antigens specific for T cells, B cells and leukocytes was studied at various ages in peripheral blood, and at 14 weeks of age in the bursa of Fabricius, spleen and thymus of two lines of chicken that had been selected over 13 generations for either high (H) or low (L) antibody responses to sheep red blood cells (SRBC), and also in a randombred control (C) line. Flow cytometry showed no consistently significant differences between the three lines in numbers of circulating lymphocytes and other leukocytes after hatching. However, higher percentages of CD4+ cells and B cells were present in the spleen and thymus from the H line compared with the L line. However, the L line was characterized by a higher proportion of splenic CD8+ cells and spleen cells expressing gamma-delta T-cell receptors. Immunization with sheep red blood cells had no effect on the distribution of CD4+ or CD8+ cells in the various tissues at 2 and 7 days after immunization. These results suggest that previously reported differences in in vivo immune responses between these chicken lines may be related to the differences in resident T-lymphocyte subpopulations in the lymphoid tissues. The involvement of T-cell subsets and non-antigen-specific mechanisms in divergent selection on humoral immune responses in chickens is discussed.

Gordon Memorial Lecture. Stress, strains and resistance

1. Stress describes the bird's defence mechanisms and a stressor is the situation that elicits the defence response. 2. As the environment can be viewed as a composite of interacting stressors, the bird's success in coping with its environment depends on the severity of the stressors and the physiological ability to respond properly and thus maintain homeostasis. 3. The neural, endocrine and more recently immune systems are considered to be integrators of the stress response. Although stress responses may be necessary for survival in wild bird populations, they are often detrimental to efficient growth, skeletal integrity and disease resistance in domesticated fowl. 4. Stress responses are modified by the genetic components.

Research note: effects of age and immunization interval on the anamnestic response to T-cell-dependent and T-cell-independent antigens in chickens

Measurement of a humoral anamnestic response is a common procedure used to evaluate immunological competence. The purposes of the present study were to determine the optimum time period between primary and secondary immunizations needed to obtain the maximum antibody titer and to determine whether this interval differs with the age of the chicken or with the type of inducing antigen. The anamnestic responses of birds of two ages to a T-cell-dependent antigen (SRBC) and to a T-cell-independent antigen (Brucella abortus, BA) were evaluated. Birds of 4 wk or 6 mo of age were injected i.v. with either BA or SRBC, and a secondary injection was given 2, 4, 6, or 8 wk later. Agglutination titers for total and mercaptoethanol (ME)-resistant antibodies were determined from serum samples collected at 3, 6, and 9 days postsecondary immunization. Generally, titers were highest at 6 days postsecondary immunization. For both antigens, the chick total antibody levels at Day 6 postsecondary immunization were higher at 4-, 6-, and 8-wk immunization intervals than at 2-wk intervals; adult titers were independent of immunization interval. There was an interaction between age of birds and type of antigen.

Production traits and alloantigen systems in lines of chickens selected for high or low antibody responses to sheep erythrocytes

The selection of chickens for high (HA) and for low (LA) antibody titers to sheep erythrocytes has produced differences in the selected trait and in the correlated responses in body weight, egg production, and erythrocyte antigens. The response to selection continued through 14 generations. There was considerable divergence between lines for erythrocyte alloantigen systems, including the major histocompatibility complex. Females from Line LA were heavier as juveniles and lighter as adults, matured at a younger age, and had higher egg production than those from Line HA. There were no differences between lines for the incidence of defective eggs laid-except for the percentage of eggs with double-yolks, which was greater for Line LA than HA. The phenotypic correlations of antibody response with growth and with reproductive traits were very low; the genetic correlations were moderate to high for most of these traits.

Genetic resistance to fowl cholera is linked to the major histocompatibility complex

Chickens of the Iowa State S1 line have been selected for ability to regress Rous sarcoma virus-induced (RSV) tumors, humoral immune response to GAT (Ir-GAT), and erythrocyte antigen B. Sublines homozygous at the major histocompatibility complex (MHC), as well as F1 heterozygotes and F2 segregants, were tested for resistance to fowl cholera by challenge with Pasteurella multocida strain X73. Control of the response at high doses was associated in a preliminary study with Ir-GAT and response to RSV tumors. Genetic control of resistance to low doses of P. multocida was demonstrated via sublines and F2 segregants to be linked with genes of the B-G region. Thus, genetic control of resistance to fowl cholera in chickens after exposure to Pasteurella multocida was shown to be linked to the major histocompatibility B complex, in this first demonstration of MHC-linked resistance to bacterial disease challenge.

Genetic and phenotypic correlations between immune response to Escherichia coli and to Newcastle disease virus vaccines

Genetic and phenotypic variation and covariation in immune response to inactivated Newcastle disease virus (NDV) vaccine and to Escherichia coli vaccine were studied in commercial poultry strains. Within any given experiment there was no tendency for individual birds to respond in a correlated manner to NDV and E. coli vaccines. There were highly significant differences between sire families in immune response to NDV vaccine (57 sire families) and to E. coli vaccine (35 sire families). Heritabilities of immune response levels to NDV and to E. coli were .41 and .25, respectively. In both cases, additive genetic standard deviations were slightly over 1.0 titer unit. The correlation between sire-family means for response to NDV and sire-family means for response to E. coli (35 sire families) was .077 and statistically nonsignificant. Thus, the data provide evidence for the presence of significant genetic variation in immune response with respect to two endemic disease antigens, but they provide no evidence for a genetic correlation in response to the two antigens.

Immune response to Newcastle disease virus vaccine, fowl-pox vaccine, and Escherichia coli vaccine in Bedouin and White Leghorn chickens

Immune response to Newcastle disease virus (NDV) vaccine, fowl pox, and E. coli vaccine was compared in the native Bedouin fowl of the Sinai desert, in a commercial Leghorn layer strain, and in the reciprocal crosses between them. Differences were not found in antibody titer levels to attenuated or inactivated NDV vaccines, in the proportion of birds showing post-vaccination immunity to fowl pox, or in the kinetics of postvaccination NDV titer levels. Rate of development of titer to Escherichia coli from day 1 to day 4, however, was significantly more rapid in Bedouin chicks than in the purebred Leghorn or the reciprocal crosses.