Wing Web Research Articles

Protective immune response of chickens to oral vaccination with thermostable live Fowlpox virus vaccine (strain TPV-1) coated on oiled rice

The objective of the present study was to develop and evaluate a local vaccine (strain TPV-1) against Fowl pox (FP) in chickens. Two separate groups of chickens were vaccinated with FP vaccine through oral (coated on oiled rice) and wing web stab routes, respectively. The results showed that the haemagglutination-inhibition (HI) antibody titres in both vaccinated groups were comparable and significantly higher (P < 0.05) than the control chickens. It was further revealed that 14 days after vaccination HI GMT of > or =2 log(2) was recorded in chickens vaccinated by oral and wing web stab routes whereas 35 days after vaccination the HI antibody titres reached 5.6 log(2) and 6.3 log(2), respectively. Moreover, in both groups the birds showed 100% protection against challenge virus at 35 days after vaccination. The findings from the present study have shown that oral route is equally effective as wing web stab route for vaccination of chickens against FP. However, the oral route can be used in mass vaccination of birds thus avoid catching individual birds for vaccination. It was noteworthy that strain TPV-1 virus could be propagated by a simple allantoic cavity inoculation and harvesting of allantoic fluid where it survived exposure at 57 degrees C for 2 hours. If the oral vaccination technique is optimized it may be used in controlling FP in scavenging and feral chickens. In conclusion, the present study has shown that FP vaccine (strain TPV-1) was safe, thermostable, immunogenic and efficacious in vaccinated chickens.

UV plumage color is an honest signal of quality in male budgerigars

AbstractElaborate and colorful feathers are important traits in female mate choice in birds. Plumage coloration can result from pigments deposited in feathers such as carotenoids and melanins, or can be caused by nano‐scale reflective tissues (structurally based coloration), usually producing ultraviolet (UV) coloration. Structural colorations remain the least studied of the three most important feather colorations. Previous studies have found a female preference for UV color in the budgerigar, Melopsittacus undulatus, but it is not clear what information this ornament conveys, nor what is the possible cost associated with its production. We investigated possible correlations between immune response and plumage color of wild‐type (green) male budgerigars. In particular we measured the wing web swelling resulting from injection of phytohaemagglutinin (PHA). We did not detect any correlation between the sedimentation rate and morphological and color variables. We found that UV chroma is the best predictor for the cutaneous immune activity. Indeed, male budgerigars with high UV reflectance in the breast feathers showed stronger immune responses. These results are consistent with the idea that UV colors are special signals conveying information about a bird's condition.

Nitric oxide production: an easily measurable condition index for vertebrates

Nitric oxide (NO) is a multifunctional signalling molecule, acting as a vasodilator, neurotransmitter, and modulator of inflammatory processes. It also participates in killing parasites, virus-infected cells, and tumor cells by formation of peroxynitrite, one of the most important initiators of the free radical damage. Uncontrolled production of NO can lead to nitrosative stress, causing damages to proteins and DNA and cell injury and death. Determination of NO production in animals is potentially informative for description of individual variation in physiological condition, health state, and work load; however, it’s potential in ecophysiological research has remained almost totally unexplored. Here, we describe application of a simple, precise, and inexpensive spectrophotometric assay for determination of NO production from 5 to 10 μL plasma samples of passerine birds. The method is based on estimation of concentrations of nitrate and nitrite—the stable end products of nitric oxide oxidation. The principle of the assay is reduction of nitrate to nitrite by copper-coated cadmium granules, followed by color development with Griess reagent. NO production in captive greenfinches (Carduelis chloris L.) was significantly repeatable over 6-day period (r = 0.35). Injection of an inflammatory agent phytohemagglutinin into wing web resulted in 21% higher levels of NO production at the third day after treatment as compared to saline-injected birds. These findings, consistently with further evidence from veterinary and biomedical literature, suggest that measuring NO production appears an efficient and robust tool for monitoring individual condition and assessment of the magnitude of innate immune response, pathogenicity of infections, and physical effort. We propose that this assay, which is easily applicable in field studies, has an excellent potential in ecophysiological research, particularly in the rapidly developing fields of immunoecology and conservation physiology.

Carotenoid‐induced maternal effects interact with ectoparasite burden and brood size to shape the trade‐off between growth and immunity in nestling great tits

1. Carotenoids are fat-soluble pigments that stimulate the immune system and can act as antioxidants. Carotenoids are thus expected to buffer the effects of environmental stressors on health. As carotenoids are a limited resource, the ability of an individual to use and metabolize carotenoids is assumed to influence its stress-resistance. Accordingly, it has been found that nestlings hatched from eggs with increased carotenoid concentration, show an enhanced ability to use carotenoids and a lower susceptibility of tissues to lipid peroxidation. 2. We tested the prediction that nestling great tits (Parus major), hatched from eggs laid by carotenoid-supplemented mothers, cope better with a transient stressor encountered after hatching. We supplemented half of the breeders with carotenoids during egg production (C+), used the other half as a control (C-), and cross-fostered the eggs between nests after clutch completion. Three days after hatching, we applied a stressor in two-third of the nests either by increasing brood size, or by infesting nests with hen fleas (Ceratophyllus gallinae) during five consecutive days. A third group was kept as a control. We then assessed the responses of C+ and C- nestlings to each stressor by measuring mass gain, body condition, plumage coloration, humoral immune response and fever response to a lipopolysaccharide injection. 3. In control nests, C+ and C- nestlings showed similar body condition but C+ nestlings had a higher increase in body temperature and tended to have a higher wing web swelling in response to lipopolysaccharide injection. Under stress, however, there were no differences in overall condition between C+ and C- nestlings. The two stressors led to different responses: when sibling competition was increased, C- nestlings favoured immune development, whereas C+ nestlings favoured mass gain and body condition, while under parasite exposure C+ and C- nestlings seemed to invest in immune development and body growth similarly. 4. Our results support the hypothesis that carotenoid-induced maternal effects provide developmental benefits under natural conditions without additional stressors. Additionally, we show that the response to sudden environmental changes depends on the environment during the initial phases of development, which thus shape phenotype and individual variation.

Sex‐Specific Effects of Handling Time on an Index of Immune Activity in Zebra Finches

Recently, there has been considerable interest in the role of the immune system in shaping life-history evolution, sexual selection strategies, and indexes of individual quality. The most frequently used assay of immune function, particularly in avian field studies, is the phytohemagglunitin (PHA) skin test. PHA is injected subcutaneously into the wing web, and the magnitude of the resultant swelling has traditionally been interpreted as an index of an individual's cell-mediated immunocompetence. The test follows one of two protocols: the traditional two-wing injection protocol, with one wing web injected with PHA and the other with phosphate-buffered saline (PBS), or the simplified one-wing protocol that omits the PBS injection. In this technical comment, we alert researchers to the importance of considering handling time when performing the PHA test. We show that zebra finches (Taeniopygia guttata) subjected to the two-wing protocol had a lower wing-web swelling than individuals injected in one wing. In males, handling time explained over 50% of the variation in an individual's skin swelling response; females were relatively unaffected by handling time. We suggest that caution should be exercised when comparing the magnitude of wing-web swelling across studies in which the alternate protocol was followed. In addition, the recording of handling time, and its inclusion in subsequent statistical analyses, may aid in the detection of subtle differences across treatments.

Correlated effects of selection for immunity in White Leghorn chicken lines on natural antibodies and specific antibody responses to KLH and M. butyricum

BackgroundThe effect of selection for three general immune response traits on primary antibody responses (Ab) to Mycobacterium butyricum or keyhole limpet hemocyanin (KLH) was studied in four experimental lines of White Leghorn chicken. Birds underwent 12 generations of selection for one of three different general immune criteria; high antibody response to Newcastle disease virus 3 weeks after vaccination (ND3), high cell-mediated immune response, using the wing web response to phytohemglutinin (PHA) and high phagocytic activity, measured as carbone clearance (CC). Line ND3-L was selected on ND3, line PHA-L was selected on PHA, and line CC-L on CC, but all lines were measured for all three traits. The fourth line was a contemporary random bred control maintained throughout the selection experiment. Principal component analysis was used to distinguish clusters based on the overall set of immune measures.ResultsIn the KLH immunised group, no differences were present between lines for natural antibodies binding to KLH and LPS, and, lines ND3-L and PHA-L had higher titers to LTA and anti-Gal titers measured before the immunisation protocol. The measure of ND3 was correlated positively with LPS titers measured post KLH immunisation and with the difference between LPS titers measured at day 0 and 7 post immunisation. In the M. butyricum immunised group, Line ND3-L showed significantly higher specific antibody response to M. butyricum, and this result agrees well with the hypothesis that the Th-1 pathway was expected to be selected for in this line.ConclusionThis study has shown that the two different antigens KLH and M. butyricum gave rise to different responses in the set of selected lines, and that the response was only enhanced for the antigen associated with the same response mechanism as that for the trait (ND3, PHA or CC) for which the line was selected. Interactions between innate and acquired immunity have been observed mainly for the high antibody selected trait, indicating there was a specific interaction due to the selection criterion. Furthermore, the results confirmed the independence between the three selected traits. Finally, principal component analysis contributed to visually discriminate high and low responders to the two new antigens in the four lines.

The structural design of the bat wing web and its possible role in gas exchange.

The structure of the skin in the epauletted fruit bat (Epomophorus wahlbergi) wing and body trunk was studied with a view to understanding possible adaptations for gas metabolism and thermoregulation. In addition, gas exchange measurements were performed using a respirometer designed for the purpose. The body skin had an epidermis, a dermis with hair follicles and sweat glands and a fat-laden hypodermis. In contrast, the wing web skin was made up of a thin bilayered epidermis separated by a connective tissue core with collagen and elastic fibres and was devoid of hair follicles and sweat glands. The wings spanned 18-24 cm each, with about 753 cm2 of surface exposed to air. The body skin epidermis was thick (61 +/- 3 microm, SEM), the stratum corneum alone taking a third of it (21 +/- 3 microm). In contrast, the wing web skin epidermis was thinner at 9.8 +/- 0.7 microm, with a stratum corneum measuring 4.1 +/- 0.3 microm (41%). The wing capillaries in the wing web skin ran in the middle of the connective tissue core, with a resultant surface-capillary diffusion distance of 26.8 +/- 3.2 microm. The rate of oxygen consumption (VO2) of the wings alone and of the whole animal measured under light anaesthesia at ambient temperatures of 24 masculineC and 33 masculineC, averaged 6% and 10% of the total, respectively. Rate of carbon dioxide production had similar values. The membrane diffusing capacity for the wing web was estimated to be 0.019 ml O2 min(-1) mmHg(-1). We conclude that in Epomophorus wahlbergi, the wing web has structural modifications that permit a substantial contribution to the total gas exchange.

Does the strength of an immune response reflect its energetic cost?

The energetic cost of immune responses has been proposed to be an important basis for trade‐offs between life‐history traits, such as between survival and reproduction. A critical assumption of this hypothesis is that the magnitude of the energetic cost increases with the strength of an immune response, so that energy can be saved by partly suppressing a response. Here, we test this assumption experimentally. The immune system of great titsParus majorwas experimentally activated by injecting different doses of phytohemagglutinin (PHA) in the wing web. We found the resting metabolic rate of immune challenged birds to increase by 5%. However, although great tits injected with a high dose had a stronger immune response, this was not paralleled by a higher metabolic rate. Thus, we found the energetic cost of the immune response to be relatively low and not dose‐dependent. This suggests to us that the energetic cost of immune responses cannot form the basis for trade‐offs between life‐history traits.

Does the strength of an immune response reflect its energetic cost?

The energetic cost of immune responses has been proposed to be an important basis for trade-offs between life-history traits, such as between survival and reproduction. A critical assumption of this hypothesis is that the magnitude of the energetic cost increases with the strength of an immune response, so that energy can be saved by partly suppressing a response. Here, we test this assumption experimentally. The immune system of great tits Parus major was experimentally activated by injecting different doses of phytohemagglutinin (PHA) in the wing web. We found the resting metabolic rate of immune challenged birds to increase by 5%. However, although great tits injected with a high dose had a stronger immune response, this was not paralleled by a higher metabolic rate. Thus, we found the energetic cost of the immune response to be relatively low and not dose-dependent. This suggests to us that the energetic cost of immune responses cannot form the basis for trade-offs between life-history traits.

Using the chicken feather as a window into cell-mediated tissue responses (99.12)

Abstract Cell-mediated immune (CMI) responses are typically tested by injecting the skin and monitoring the skin reaction. In chickens, various integumental tissues are suitable to measure the CMI reaction, including the wattle, wing web, toe web and foot pad. Using the Smyth line chicken vitiligo model to study the spontaneous autoimmune destruction of pigment cells in feathers, we have found that one growing feather-tip (3 mm diameter by 8 mm length) yields generous amounts of material for down-stream gene-expression-, histological-, and cell population-analyses. Moreover, growing feathers are easily accessible for microinjection, removal of a feather is minimally invasive, and feathers are very suitable for repeated sampling during an immune response. To investigate the potential of the feather as a window into tissue immune responses, time-course studies were conducted comparing leukocyte infiltration in wattles, wing webs and growing feathers in response to injection of vehicle, PHA or LPS, and during the recall response to Mycobacterium butyricum. Based on histology and immunohistochemical staining, leukocyte infiltration profiles over a 72 hour period were similar in all three tissues tested. Hence, the feather provides excellent opportunity to monitor and assess CMI responses and immunomodulation strategies in situ and via down-stream analyses. Support: Arkansas Experiment Station Animal Health Grant

Maternal and dietary carotenoids interactively affect cutaneous basophil responses in growing chickens ( Gallus gallus domesticus)

This trial examined effects of lutein supplied from maternal (i.e., in ovo) and dietary routes on cutaneous basophil hypersensitivity responses in chickens. Chicks hatched from one of two in ovo carotenoid levels ( n = 100/level; carotenoid-replete or carotenoid-deplete eggs) were fed one of two diet lutein levels (0 or 40 mg diet lutein/kg diet). At 14 d post-hatch, phytohemagglutinin (PHA) was injected into the wing web, and thickness and leukocyte populations were measured at 0 to 48 h. PHA increased wing web thickness at 4 to 48 h post-PHA ( p < 0.05), and the swelling response was most related to macrophage numbers in the wing web. Swelling occurred more rapidly in chicks from carotenoid-deplete eggs ( p < 0.05), but eventually reached a greater thickness in chicks from carotenoid-replete eggs ( p < 0.05). Differences in leukocyte infiltration occurred due to diet and in ovo carotenoid exposure, and indicate that pre- and post-hatch carotenoid exposure had additive or synergistic effects on the PHA-induced wing web response. Evaluation of the cellular contents of the injection site is a much better indicator of the immunomodulatory effects of lutein than measurements of the amount of swelling.

Reproductive State, but Not Testosterone, Reduces Immune Function in Male House Sparrows (Passer domesticus)

The immune system requires energetic and nutritional resources to optimally defend organisms against pathogens and parasites. Because resources are typically limited, immune function may require a trade-off with other physiologically demanding activities. Here, we examined whether photoperiodically induced seasonal states (breeding, molting, or nonbreeding) affected the cutaneous immune response of captive male house sparrows (Passer domesticus). To assess immune function in these birds, we injected the mitogen phytohemagglutinin (PHA) into the patagium and measured the resulting wing web swelling. Molting and nonbreeding birds had similar immune responses to PHA injection. However, males in a breeding state showed lower immune responses than both molting and nonbreeding birds even though they did not actually breed. We tested whether this decrease in the PHA swelling response in birds in a breeding state was due to elevated plasma concentrations of testosterone (T) by administering T to birds in a nonbreeding state. Contrary to some evidence in the literature, T did not suppress the response to PHA in house sparrows. Our data show that passerine birds show seasonal modulation in immune function, even in benign environmental conditions. However, even though T is often cited as a strong immunosuppressant, it is not fully responsible for this seasonal modulation.

Genetic analysis of the growth curve of Rous sarcoma virus-induced tumors in chickens

White Leghorn chicks homozygous for B19 MHC haplotype were selected for 18 generations on tumor regression after inoculation in the wing web with an SR-D strain of Rous sarcoma virus (RSV) at 4 wk of age. Each chick was assigned a tumor profile index (TPI) based on age at death and size of the tumor. During 18 generations, 2,010 birds were divergently selected on TPI for either progression or regression of the tumor (P and R lines). A Brody growth curve was fitted for each bird. Brody function parameters included the asymptotic tumor volume (A), the factor for increased growth in progression phase (K1), the factor for decreased growth in regression phase (K2), age at maximum volume (Tmax), and maximum volume of the tumor (Vmax). Tumor growth curves were found to be different according to line, sex, and restriction fragment pattern Y complex Rfp-Y MHC haplotype (Yw*15, Yw*16, and Yw*17). Within the P line, birds from the Yw*16 haplotype reached Vmax at an earlier age than Yw*15 and Yw*17, but with a lower Vmax value. Within the R line, tumor growth curves of birds from Yw*16 and Yw*17 haplotypes were similar. Rank correlations between the different parameters and TPI were low (between -0.26 and 0.36). Heritability estimated by the sire component was high for Vmax (0.73). Heritabilities of Tmax and K2 were moderate (0.20 to 0.23 for Tmax and 0.18 to 0.21 for K2) allowing these traits to be used as selection criteria. Heritabilities of A and K1 were lower than 0.12. Modeling the growth curve should contribute to better distinction between progressors and regressors.

Investigating the turkey's ‘snood’ as a morphological marker of heritable disease resistance

SummaryThe sexual ornamentation of many wild species, including the ancestors of domestic poultry, are reliable indicators of parasite burden, suggesting that they may serve as morphological markers of heritable disease resistance. Measures of male ornamentation might be a culturally and economically feasible method of identifying conservation‐worthy genotypes from indigenous poultry flocks. Here we investigate the relationship between the sexually selected, parasite‐burden‐indicating ‘snood’ of male game farm turkeys, and their immunocompetence and immunogenetic [major histocompatibility complex (MHC) class II B restriction fragment‐length polymorphism (RFLP)] variation. We find that specific restriction fragments appear to be favourable to both immunocompetence and ornament size, but that turkey snood length is not a valuable predictor of wing web swelling due to phytohemagglutinin (PHA) injection. Immunocompetence increased with composite band sharing, a measure of absolute variation at the MHC. Snood length, however, was greatest in males that showed intermediate measures of relative band sharing. We conclude that tradeoffs among the conflicting demands on the energy reserves of free‐living poultry, might ensure that long‐snooded indigenous turkeys are best adapted to local disease conditions without wasting resources on hyperimmunity.

Cell-mediated immune response affects food intake but not body mass: An experiment with wintering great tits

:Reduction in body mass is one of the major energetic costs associated with immune challenge. In studies where such findings have been obtained, birds performed their normal activities in a natural environment during the experiments. In such situations food intake after immune challenge was not controlled. Therefore, reduction in body mass could be due to a reduction in foraging activity through difficulties in searching for and finding food. The aim of the present study is to determine whether an immune challenge affects body mass or food intake in wintering great tits maintained in captivity. Ten individuals were kept in an outdoor aviary during the experiments. Cell-mediated immunity was determined by the wing web index using phytohemagglutinin (PHA) injection. Body mass and food intake were measured before and after PHA injection. We found no difference in body mass between pre- and post-PHA injection. However, we found a significant increase in the amount of food intake after PHA injection compared with food intake before injection. Moreover, the magnitude of the immune response, measured by the wing web index, was positively related to the amount of food intake. In conclusion, our results suggest that the immune response to PHA is a costly task for small birds during winter and that this cost is compensated for by the increase in food intake.

Immune activity elevates energy expenditure of house sparrows: a link between direct and indirect costs?

The activation of an immune response is beneficial for organisms but may also have costs that affect fitness. Documented immune costs include those associated with acquisition of special nutrients, as well as immunopathology or autoimmunity. Here, we test whether an experimental induction of the immune system with a non-pathological stimulant can elevate energy turnover in passerine birds. We injected phytohaemagglutinin (PHA), a commonly used mitogen that activates the cell-mediated immune response, into the wing web of house sparrows, Passer domesticus. We then examined energetic costs resulting from this immune activity and related those costs to other physiological activities. We found that PHA injection significantly elevated resting metabolic rate (RMR) of challenged sparrows relative to saline controls. We calculated the total cost of this immune activity to be ca. 4.20 kJ per day (29% RMR), which is equivalent to the cost of production of half of an egg (8.23 kJ egg(-1)) in this species. We suggest that immune activity in wild passerines increases energy expenditure, which in turn may influence important life-history characteristics such as clutch size, timing of breeding or the scheduling of moult.

Maternal dietary N-3 fatty acids alter the spleen fatty acid composition and bovine serum albumin-induced wing web swelling in broilers

Effects of maternal dietary polyunsaturated fatty acids (PUFA) on the spleen fatty acid composition and BSA-induced wing web swellings were investigated in broilers. One hundred twenty broiler breeder hens 26 wk of age were randomly assigned to diets containing mainly wheat, corn, soy meal, barley, oat and 5% (wt/wt) added sunflower oil, fish oil, or a mix of sunflower and fish oils (1:1). After 2 wk on the experimental diets, birds were inseminated, eggs were collected and incubated. Progeny chicks were then fed identical diets for 6 wk. The maternal dietary oils affected (P < 0.05) n-6 and n-3 PUFA in the spleens of hatching chicks. After 2 wk, n-6 PUFA did not differ among the groups; n-3 PUFA, docosapentaenoic, and docosahexaenoic (DHA) acids were higher (P < 0.05) in the spleens of broilers from hens fed 2.5 or 5% fish oil. After 4 wk, broilers from hens fed 5% fish oil still had higher levels of DHA (P < 0.05) in their spleens than those from hens fed 5% sunflower oil. The BSA-induced wing web swelling response was suppressed (P < 0.05) by n-3 PUFA in breeder hens. Broilers from hens fed high levels of n-3 PUFA had lower (P < 0.05) wing web swelling reactions to BSA at 2 wk (2.5% fish oil) and 4 wk (2.5 and 5% fish oil). In conclusion, n-3 PUFA in breeder hen diets suppressed the BSA-induced wing web swellings of the hens, increased the spleen n-3 fatty acids (especially DHA), and decreased BSA-induced wing web swellings of progeny up to 4 wk of age.

Construction and immunogenicity studies of recombinant fowl poxvirus containing the S1 gene of Massachusetts 41 strain of infectious bronchitis virus.

The spike 1 (S1) surface glycoprotein of infectious bronchitis virus (IBV) is the major inducer of the generation of virus neutralizing antibodies, and the administration of purified S1 has been shown to elicit a protective immune response against virulent virus challenge. On the basis of these observations, recombinant fowl poxvirus (rFPV) containing a cDNA copy of the S1 gene of IBV Mass 41 (rFPV-S1) was constructed and its immunogenicity and vaccine potential were evaluated. Initially, rFPV-S1 was shown to express the S1 in vito by indirect immunofluorescence staining and western blot analyses. Later, in vivo expression was demonstrated by the detection of IBV-specific serum immunoglobulin G and neutralization antibodies in the sera of chickens immunized with rFPV-S1. That the recombinant virus elicited anti-IBV protective immunity was indicated by the manifested, relatively mild clinical signs of disease, decreased titers of recovered challenge virus, and less severe histologic changes of the tracheas in virulent IBV Mass 41-challenged chickens previously receiving rFPV-S1 as compared with parental fowl poxvirus (FPV)-vaccinated control birds. In contrast, chickens immunized with either recombinant or parental FPV were resistant to a subsequent virulent FPV challenge. As to a preferred method of immunization, wing web administration appeared to be superior to the subcutaneous route because a greater percentage of birds vaccinated by the former protocol exhibited an anti-IBV humoral immune response. Thus, rFPV-S1 has potential as a poultry vaccine against both fowl pox and infectious bronchitis.

Effects of testosterone on cell-mediated and humoral immunity in non-breeding adult European starlings

One of the primary assumptions of the immunocompetence hypothesis is that testosterone is immunosuppressive. Although many studies in birds and mammals have supported this assumption, conflicting results have been reported in a variety of species. We investigated the effects of testosterone manipulation on both cell-mediated and humoral immunity in adult songbirds, European starlings (Sturnus vulgaris). Male and female starlings were wild-caught, housed in the laboratory, and implanted with either empty silastic capsules or capsules containing testosterone. Six weeks after implantation, humoral immunity was assessed by injecting the birds with a novel antigen, keyhole limpet hemocyanin, and measuring specific antibody responses 10 and 15 days later via an enzyme-linked immunosorbant assay. Cell-mediated immunity was assessed 7 weeks after implantation via intradermal injection of the T-cell mitogen phytohemagglutinin into the wing web and measuring the degree of swelling 24 h later. Antibody responses to antigenic challenge were significantly suppressed in testosterone-treated females 10 days post-injection and in both sexes 15 days post-injection. Furthermore, there was a significant inverse relationship between individual variability in antibody responsiveness and plasma testosterone concentrations. Cell-mediated responses to phytohemagglutinin stimulation were also significantly suppressed in testosterone-treated males compared to same-sex controls. Testosterone treatment significantly increased plasma corticosterone concentrations compared to controls, and the possibility of this effect mediating the immunosuppressive effects of testosterone is discussed. The present study is among the first to demonstrate testosterone-induced suppression of both cell-mediated and humoral immunity in a species of songbird.

Health impact of phytohaemagglutinin-induced immune challenge on great tit (Parus major) nestlings

Assuming that immune function is resource-limited, it can be expected to compete with other important functions of an organism for the total resource pool, giving rise to trade-offs in resource allocation. To test whether such a trade-off exists between immune defence and growth, the physiological impact of an immune challenge was examined in great tit (Parus major) nestlings, using phytohaemagglutinin (PHA) as a novel antigen. Nestlings injected intradermally with PHA in wing webs at 8 days of age produced a heterophilic response, while their growth was not suppressed in comparison with untreated control siblings. Nestlings that grew poorly produced a weaker cutaneous response to PHA inoculation than well-growing nestlings. These two results suggest that the response to PHA (a measure of the intensity of T-lymphocyte mediated immune responsiveness) is resource demanding, but these resources are not reallocated from those used for growth. This finding can be reconciled with current hypotheses, which propose that the currency in trade-offs between immune response and other demands on the organism is not necessarily energy or macronutrients but may instead be based on immunopathology, carotenoids, or production of free radicals.