Age-related changes in pro-inflammatory cytokines, acute phase proteins and cortisol concentrations in neonatal piglets

Concentrations of selected immunological parameters in the serum and processing fluid of suckling piglets and the serum and colostrum of their mothers

BACKGROUND

Blood sampling from neonatal piglets is related to multiple disadvantages. Therefore, a new, alternative matrix is required to assess piglets' early immune status efficiently. The present study aimed to assess the usefulness of processing fluid for determining selected piglets' immune parameters. 264 pigs - 31 sows, 146 male piglets, and 87 female piglets from commercial indoor farrow-to-finish pig herd were included in this study. 264 serum, 31 colostrum, and 146 processing fluid samples were collected. Serum was collected from all animals, colostrum was collected from sows, and processing fluid was collected from male piglets only. Using commercial ELISA tests, the concentration of various immunoglobulins, cytokines, and acute phase proteins was assessed in each matrix. Statistical analyses were employed to determine differences in the concentration of measured indices between piglets' serum and processing fluid and correlations in the concentration of tested indices between particular sets of matrices.

RESULTS

Statistical analyses did not reveal significant differences in the IgG, IgA, IL-1β, IL-4, IL-6, and IFN-γ concentration between piglets' serum and processing fluid (p > 0.05). A positive correlation (p < 0.05) regarding the concentration of some indices between processing fluid and samples collected from sows was also observed.

CONCLUSIONS

Processing fluid can be considered a promising alternative to blood for assessing some immunological indices in piglets, such as IgG, IgA, IL-1β, IL-4, IL-6, and IFN-γ, and, possibly, in the indirect assessment of some indices in lactating sows, including IgA, IL-1β, IL-4, IL-6, IL-8, IFN-γ, or Pig-MAP.

A Comparison of Haematological and Biochemical Profiles between Intrauterine Growth Restriction and Normal Piglets at 72 Hours Postpartum

Intrauterine growth restriction in piglets has been a problem in the pig industry due to genetic selection based on hyperprolificacy. This has led to an increase in the number of underweight piglets and a worsening of the survival rate. The goal of this study was to enhance the knowledge of differences between normal and IUGR piglets a few hours after birth in terms of haematological variables, biochemical parameters, and immunoglobulin levels. Two groups of 20 piglets each were assessed. The control group (N) was made up of piglets with weights greater than 1500 g, and the IUGR group consisted of piglets weighing 500-1000 g and with at least two IUGR features. Blood samples were collected 72 h after birth for analysis of the red and white blood cell parameters, reticulocyte indices, platelet indices, biochemical parameters, and immunoglobulin levels. Alterations in red blood cells and reticulocytes, a lower lymphocyte count, hyperinsulinemia, and high oxidative stress were observed in IUGR piglets (p < 0.05). In contrast, differences were not observed (p > 0.05) in the serum immunoglobulin level. It can be concluded that the haematological and biochemical differences in IUGR piglets with respect to normal-weight piglets are present at birth indicating possible alterations in immunity, metabolism, and redox status; therefore, IUGR piglets could be more vulnerable to illness and future disorders, such as metabolic syndrome.

Influence of the circadian cycle, sex and production stage on the reference values of parameters related to stress and pathology in porcine saliva

BACKGROUND

The concentration of biomarkers in saliva could be influenced by several factors not related to the specific condition under analyses, which should be considered for proper clinical interpretation. In the present study, the circadian rhythm of C-reactive protein (CRP), haptoglobin (Hp), Pig-MAP, S100A12, Cu, Zn, Adenosine deaminase (ADA), total protein (TP), total antioxidant capacity (TAC), total oxidant status (TOS), oxidative stress index (OSI), cortisol and α-amylase in saliva of 20 female and 20 male pigs was investigated. Moreover, the influence of sex and production phase (post-weaning, fattening and finishing) on the concentrations of biomarkers in a total of 414 healthy pigs was studied and the reference intervals for all salivary biomarkers were calculated accordingly.

RESULTS

All parameters except Pig-MAP, OSI and α-amylase varied significantly along the daytime, and most of them peak around early afternoon (13-15 h). The cosinor analysis described the temporal dynamics of circadian rhythms for all parameters. The range values showed differences between male and female pigs in 8 out of the 13 biomarkers, with higher concentrations in females in comparison to male pigs. The influence of the production phase on the salivary concentrations was observed for all the biomarkers. The highest concentrations were observed for Pig-MAP, S100A12 and α-amylase in post-weaning animals, for TP in growing pigs and for OSI in finishing animals. Most of the sex-influenced biomarkers showed the highest concentrations at growing stages with some exceptions such as ADA or Hp that showed the peak at finishing and post-weaning stages respectively.

CONCLUSIONS

It is necessary to establish the optimal daytime for routine saliva sampling to avoid circadian variations and for that end, the time interval between 10:00 a.m. to 12:00 a.m. is highly recommended. The factors sex and production phase influence the concentration of biomarkers and should be considered for proper biomarker interpretation. The reference intervals presented here for each salivary biomarker will help to correctly interpret the results of these analytes and contribute to the use of saliva as a non-invasive sample for the diagnosis and monitoring of the health status of swine farms.

TLR4, MyD88, and TNF-α Expression in the Lungs of Akkaraman and Romanov Lambs in Response to LPS and LTA

Toll-like receptors are involved in the recognition of bacterial toxins, which cause infection in the respiratory system. This study aimed to evaluate microanatomical and histological alterations in the lungs of 24 healthy Akkaraman and Romanov lambs after the administration of lipoteichoic acid (LTA), lipopolysaccharide (LPS), and LTA + LPS and investigate the gene, protein, and immune expression levels of TLR4, MyD88, and TNF-α molecules, known to have immune functions. Microanatomical examinations showed thickened peribronchial and alveolar walls in the lungs of groups LTA, LPS, and LTA + LPS of both breeds due to immune cell infiltration. TLR4, MyD88, and TNF-α immunoexpressions were positive to varying degrees in the cytoplasm and nucleus of the bronchial and bronchiolar luminal epithelial cells, alveolar epithelial cells, and alveolar macrophages. TLR4 and TNF-α protein expressions were statistically different in the LPS-treated Romanov lambs, compared to the other groups. Among the Akkaraman lambs, TLR4 gene expression was significantly higher in group LPS, and among the Romanov lambs, TLR4, MyD88, and TNF-α gene expressions were significantly higher in group LTA + LPS. Therefore, TLR4, MyD88, and TNF-α molecules, involved in the immune response, were found to be expressed at different levels against LTA and LPS in the lungs of two different sheep breeds.

Immune status of piglets during the first week of life: Current knowledge, significance and assessment

The immune system of neonate piglets differs from adult pigs in structure and competence. Although piglets are born immunocompetent, they are genuinely immunologically defenceless. To survive in the environment, piglets need passive protection provided by sow’s colostrum and milk when constantly exposed to numerous pathogens. Early assessment of piglets’ immune status may enable rapid intervention in case of detection of any deficiencies or disorders. Moreover, awareness of the piglets’ immunocompetence and the level of maternally-derived antibodies (MDA) may allow the creation of a proper vaccine schedule. Hence, extending knowledge of prenatal ontogeny of the porcine immune system, the immune status of neonate piglets’ and the immunological components of porcine colostrum is crucial. Since animal welfare has become a more critical element of animal production, new, non-invasive sampling methodologies are highly desirable for the evaluation of piglets’ immune status.

Haptoglobin and C-Reactive Protein-Non-specific Markers for Nursery Conditions in Swine

A quality concept for production in the pork market includes granting a good health status of pigs from birth to slaughter. This concept is a precondition for animal welfare as well as reducing antibiotic usage in farm animals. The demand for fighting bacterial antimicrobial resistance in humans, animals, and in the environment is one driving force for the development of innovative technical solutions to improve husbandry. Maintenance of a good health status in pigs depends on early detection of a disturbance in homeostasis in critical phases of life. This can be measured by non-specific biomarkers as acute phase proteins. In this project, husbandry conditions and health status in nursery pigs were monitored in an autumn and winter nursery period from weaning to the end of nursery in two compartments with 180 pigs each. It was investigated whether a slight modification in indoor climate achieved by a new ammonia sensory technology coupled with the electronic control unit of the forced ventilation system ensuring ammonia levels lower than 5 ± 3 ppm in one compartment led to a better health status in piglets in comparison to the control compartment. In the examined nursery periods in different seasons, ammonia concentrations in the experimental compartment were significantly lower than in the control compartment, thus proving the functionality and efficacy of the technical system. Production parameters as feed conversion rate and average daily weight gain were slightly improved in the experimental compartment without implementing other measures. Multifactorial analysis of variance resulted in a significant influence of season, daily quarter, and compartment on ammonia concentration. The challenge to preserve a high health status of piglets also during suboptimal outside climate in the transitional season was reflected by an increase in the acute-phase proteins haptoglobin (Hp) and C-reactive protein (CRP) in autumn compared to winter. The seasonal influence on concentrations of CRP and Hp superimposed potential influences of the climate modification. New technological concepts to reduce noxious gases and dust in the animal environment as well as emissions, which in parallel guarantee optimal temperatures also during extreme weather conditions, can be evaluated by clinical data in combination with biomarkers.

Porcine Breed, Sex, and Production Stage Influence the Levels of Health Status Biomarkers in Saliva Samples

In this study, the influence of several factors such as breed, sex, and production stage over the normal range values of salivary biomarkers of health status was evaluated in pigs. A total of 409 pigs of 2 different breeds (conventional Large White × Duroc and Iberian pigs) were included in the study. Animals were divided into different groups according to their sex (male or female) and the stage of the production cycle they were in (post-weaning, nursery, fattening, and finishing). The levels of an inflammatory marker, adenosine deaminase (ADA), and two acute phase proteins, C-reactive protein (CRP) and haptoglobin (Hp) were measured in saliva samples. Moreover, the total antioxidant capacity level (TAC) was quantified for the first time in porcine saliva; therefore, an analytical validation and stability analysis during storage at −80°C were also performed. Differences according to breed were observed for all the markers studied; thus, the influence of age and sex on the normal range values were studied separately for conventional and Iberian pigs. In Large White × Duroc pigs the overall median values of ADA, CRP, Hp and TAC were 282 U/L, 10.49 ng/mL, 0.88 μg/mL, and 21.73 μM Trolox equivalents, respectively. However, higher values of inflammatory marker and acute phase proteins were observed in males at the initial stages of the production cycle, while females presented higher values when they had reached sexual maturity. In Iberian pigs the overall median values observed were 585 U/L, 4.81 ng/mL, 0.63 μg/mL, and 21.21 μM Trolox equivalents for ADA, CRP, Hp, and TAC respectively with slight differences in the influence of the studied factors. Sex differences were not observed in the levels of acute phase proteins in Iberian pigs, probably due to the castration of males during the first days of life; however, ADA levels were found to be higher in male pigs at the end of the production cycle. It could be concluded that breed, sex, and production stage influence the range values of salivary markers of health status in pigs and should be taken into account to further establish reference intervals.

Late gestation diet supplementation of resin acid-enriched composition increases sow colostrum immunoglobulin G content, piglet colostrum intake and improve sow gut microbiota

Resin acid-enriched composition (RAC) mainly containing tall oil fatty acid with an active component of resin acid (RA) can improve the microbial population in the digestive system, change the microbial fermentation, and improve the feed conversion ratio. We investigated the effects of dietary supplementation of RAC on sow colostrum yield (CY), colostrum composition and gut microbiota. Tall oil fatty acid and RA are commonly termed RAC and CLA, pinolenic, abietic, dehydrobiotic acids are characteristic components of RAC. The experiment was conducted in three trials in three respective herds. Sows were fed with a control diet and the same diet supplemented with 5 g RAC/day per sow during the last week of gestation. The 16S ribosomal RNA gene sequencing technique was used to assess sows' faecal microbiota populations at farrowing. Colostrum nutritional composition, acute phase proteins (APPs) and immunoglobulin (Ig) content were also assessed. Individual piglets were weighed at birth and 24 h after the birth of first piglets in order to calculate CY and later at 3 to 4 weeks to calculate average daily gain. The RAC-fed sows had significantly higher IgG levels (P0.05), but those fed RAC had higher levels of colostrum serum amyloid A. Colostrum yield was significantly higher in RAC-fed sows in herds 2 and 3 with heavier piglets between 3 and 4 weeks of age (P0.05). Resin acid-enriched composition supplementation significantly increased some beneficial and fermentative bacteria (Romboutsia and Clostridium sensu stricto) than the control diet (P<0.01) while some opportunistic pathogens (Barnesiella, Sporobacter, Intestinimonas and Campylobacter), including Proteobacteria, were suppressed. Therefore, RAC added to the sow diet at late pregnancy increases colostrum IgG, colostrum availability for neonate piglets, and seems to promote better maternal intestinal microbial sources.

Time course study of the response to LPS targeting the pig immune gene networks

Background

Stress is a generic term used to describe non-specific responses of the body to all kinds of challenges. A very large variability in the response can be observed across individuals, depending on numerous conditioning factors like genetics, early influences and life history. As a result, there is a wide range of individual vulnerability and resilience to stress, also called robustness. The importance of robustness-related traits in breeding strategies is increasing progressively towards the production of animals with a high level of production under a wide range of climatic conditions and management systems, together with a lower environmental impact and a high level of animal welfare. The present study aims at describing blood transcriptomic, hormonal, and metabolic responses of pigs to a systemic challenge using lipopolysaccharide (LPS). The objective is to analyze the individual variation of the biological responses in relation to the activity of the HPA axis measured by the levels of plasma cortisol after LPS and ACTH in 120 juvenile Large White (LW) pigs. The kinetics of the response was measured with biological variables and whole blood gene expression at 4 time points. A multilevel statistical analysis was used to take into account the longitudinal aspect of the data.

Results

Cortisol level reaches its peak 4 h after LPS injection. The characteristic changes of white blood cell count to LPS were observed, with a decrease of total count, maximal at t=+4 h, and the mirror changes in the respective proportions of lymphocytes and granulocytes. The lymphocytes / granulocytes ratio was maximal at t=+1 h. An integrative statistical approach was used and provided a set of candidate genes for kinetic studies and ongoing complementary studies focused on the LPS-stimulated inflammatory response.

Conclusions

The present study demonstrates the specific biomarkers indicative of an inflammation in swine. Furthermore, these stress responses persist for prolonged periods of time and at significant expression levels, making them good candidate markers for evaluating the efficacy of anti-inflammatory drugs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-4363-5) contains supplementary material, which is available to authorized users.

Age-associated differential production of IFN-γ, IL-10 and GM-CSF by porcine alveolar macrophages in response to lipopolysaccharide

The aim of the present study was to investigate the age-related production variation of T helper (Th)-type cytokines (IL-2, IL-4, IFN-γ and IL-10), granulocyte macrophage-colony stimulating factor (GM-CSF) and nitric oxide (NO) by lipopolysaccharide (LPS)-stimulated porcine alveolar macrophages (AMs) in a time-dependent manner. For this purpose, AMs were isolated from 5-days (newborn), 40-days (post-weaned) and 120-days (young) old pigs. Cells were incubated for 24h in the absence or presence of increasing concentrations of LPS (0.0, 0.01, 1.0, 5.0 and 10.0 μg/mL). IL-10, IFN-γ and GM-CSF mRNA expression was upregulated in a dose-dependent manner for all age groups (P<0.05). Age-related differences included a significantly increased IL-10 mRNA and protein production in newborn piglets compared to post-weaned and young pigs. IL-10 production pattern was similar with a higher peak between 12 and 36 h post-induction in all age groups. In contrast, IFN-γ mRNA and protein level was significantly elevated in young pigs 12h and 24h post-induction, respectively, while the time course production of IFN-γ was mostly consistent in newborn and post-weaned piglets. GM-CSF mRNA expression was significantly lower in newborn piglets than in post-weaned and young pigs. The kinetic of GM-CSF expression peaked at 12h in young and post-weaned pigs and at 24h in newborn piglets. IL-4 mRNA levels were very low and no apparent change of IL-2 expression was observed following LPS stimulation in all age groups. Only very low levels of NO were detected in the cell supernatants of young pigs. Collectively, these studies suggest age-related differences in time-dependent production of IL-10, IFN-γ and GM-CSF by porcine AMs with potential immunoregulatory consequences to be explored further.

Age-related changes in phagocytic activity and production of pro-inflammatory cytokines by lipopolysaccharide stimulated porcine alveolar macrophages

The aim of the present study was to determine the age-related changes of phagocytic capacity and the kinetic production of cytokines in lipopolysaccharide-stimulated porcine alveolar macrophages. For this purpose, AMs were isolated from 5 (newborn), 40 (post-weaned) and 120 (young) day old pigs. Results of phagocytosis assay showed that AMs from newborn piglets had less phagocytic capacity than those of young pigs (P<0.05). For the kinetics study, cells and supernatant were collected at 1, 6, 12, 24, 36 and 48 h after LPS stimulation for quantification of cytokine mRNA and protein by quantitative real-time PCR and ELISA, respectively. The kinetics results showed that AMs from newborn piglets were significantly less capable of producing IL1β, IL6, IL12β, TNFα and IL8 than post-weaned piglets or young pigs. IL18 mRNA did not show significant differences between ages. MIP2 and MCP1 mRNA was higher in young pigs. Hence, higher production of cytokines by AMs may be the surfactant factors in the pulmonary host defense system. These results indicate that AMs from newborn piglets might be functionally immature, which may lead to increased susceptibility to lung infections. Future studies of cytokine kinetics in more animals are clearly needed to confirm these results across a wider age range.

Expression of Toll-like receptors and downstream genes in lipopolysaccharide-induced porcine alveolar macrophages

The aim of the present study was to determine the age-related kinetic changes of Toll-like receptors (TLRs) and downstream genes expression, and secretion of cytokine in lipopolysaccharide (LPS) stimulated porcine alveolar macrophages (AM). For this purpose, AMs were isolated from 5-day-old newborn piglets and 120-day-old young pigs. mRNA expression and cytokine measurement was determined by quantitative real-time PCR and ELISA, respectively. First, AMs were incubated for 24 h in the absence or presence of increasing concentrations of LPS. Results showed the up-regulation of TLRs 2, 4, 5 and 9 mRNA from all concentrations of LPS used, as compared to non-stimulated cells, and TLR4 was the highest expression in both ages (P<0.05). Furthermore, quantitative analysis demonstrated increased expression of mRNAs encoding TLRs 2, 4, 5 and 9, LBP, CD14, MD2, MyD88, IRAK4 and TRAF6 in both ages in a time-dependant manner (P<0.05). Overall, LPS inducible mRNA for TLR4, LBP, CD14 and MyD88 had higher expression in newborn piglets compared with those of young pigs (P<0.05). The level of cytokine protein IL6 and TNFα in supernatant fluid significantly varied with time of incubation and age of animals. Their concentration increased immediately at 1 h after LPS stimulation and remained significantly higher up to 48 h in both ages. Production of pro-inflammatory cytokine protein IL6 and TNFα in supernatant was significantly higher in young pigs than those of piglets. This study suggests that differential age-related changes in the expression of TLRs and downstream genes, and pro-inflammatory cytokine could contribute to a different age-related innate immune response during pulmonary infection. Further investigation is warranted to determine the precise effects of LPS on porcine AMs by means of a functional study across a wider age range.

Growth, clinical chemistry and immune function in domestic piglets fed varying ratios of arachidonic acid and DHA

In the USA, infant formulas contain long-chain PUFA arachidonic acid (ARA) and DHA in a ratio of 2:1 and comprise roughly 0·66 g/100 g and 0·33 g/100 g total fatty acids (FA). Higher levels of dietary DHA appear to provide some advantages in visual or cognitive performance. The present study evaluated the effect of physiologically high dietary ARA on growth, clinical chemistry, haematology and immune function when DHA is 1·0 g/100 g total FA. On day 3 of age, formula-reared (FR) piglets were matched for weight and assigned to one of six milk replacer formulas. Diets varied in the ratio of ARA:DHA as follows (g/100 g FA/FA): A1, 0·1/1·0; A2, 0·53/1·0; A3-D3, 0·69/1·0; A4, 1·1/1·0; D2, 0·67/0·62; D1, 0·66/0·33. A seventh group was maternal-reared (MR) and remained with the dam during the study. Blood collection and body weight measurements were performed weekly, and piglets were killed on day 28 of age. No significant differences were found among any of the FR groups for formula intake, growth, clinical chemistry, haematology or immune status measurements. A few differences in clinical chemistry, haematology and immune function parameters between the MR pigs and the FR groups probably reflected a difference in growth rate. We conclude that the dietary ARA level up to 1·0 g/100 g total FA is safe and has no adverse effect on any of the safety outcomes measured, and confirm that DHA has no adverse effect when ARA is at 0·66 g/100 g FA.

Transfer of maternal haptoglobin to suckling piglets

The acute phase protein haptoglobin (Hp) exerts immune modulating functions in the innate and adaptive immune system. In pigs, serum Hp concentrations are linked to impaired growth performance. There is little information on Hp in newborn piglets and the onset of endogenous Hp synthesis. In the first experiment we analyzed Hp concentrations in colostrum from sows (n=5) and serum from their off-spring (n=43) during the first 12h of life. The piglets were divided in a colostrum group which was allowed to suckle and a colostrum-deprived group which received a Hp-free milk replacer. We were able to show that serum Hp in newborn piglets increased 3h after colostrum intake whereas serum Hp remained low in colostrum-deprived littermates. The absorption of colostral Hp in the jejunum could be shown via immunohistochemistry. In colostrum suckled piglets, endogenous Hp synthesis in the liver increased 9h after birth, no increase in Hp mRNA was observable during the first 12h of life in colostrum-deprived piglets. From our results we concluded that maternal Hp is transferred to newborn pigs via colostrum and the stimulus for the increase in Hp synthesis is mediated by colostrum. In a second experiment we analyzed Hp in colostrum, milk and serum from sows (n=43) and their off-spring (n=442) from birth until weaning. Haptoglobin was high in colostrum (1.11 ± 0.10mg/ml) and declined to lower but stable milk levels (0.36 ± 0.08 mg/ml) until weaning. Colostral Hp and daily litter weight gain were negatively correlated (r=-0.5, p<0.01) whereas the relationship between piglets serum Hp and daily weight gain was weaker (r=-0.22, p<0.05). We therefore speculate that maternal Hp exerts systemic actions in piglets.

Effects of different antimicrobial treatments on serum acute phase responses and leucocyte counts in pigs after a primary and a secondary challenge infection with Actinobacillus pleuropneumoniae

The susceptibility to an initial challenge and a re-challenge inoculation with Actinobacillus pleuropneumoniae was analysed in pigs that were treated with antimicrobials of different efficacies following the first exposure to A pleuropneumoniae. In brief, 30 nine-week-old specific pathogen-free pigs were allocated to five groups of six. After acclimatisation, four groups were inoculated with A pleuropneumoniae serotype 2. At the onset of clinical signs, three of the groups of pigs were treated with enrofloxacin, tetracycline or penicillin. A fourth group served as the inoculated control and the fifth group as a control group that had not been inoculated. On day 28, all five groups were re-challenged with the same strain of A pleuropneumoniae serotype 2 as had been used in the first inoculation. No treatments were carried out at this time. The acute phase responses and differential leucocyte counts were monitored in detail after both inoculations. Leucocytosis and acute phase responses in the forms of serum amyloid A, pig-major acute phase protein and haptoglobin were recorded in all of the inoculated groups after the onset of clinical signs following the first inoculation. A porcine mannan-binding lectin-A response was less evident in the pigs. Acute phase responses resembling those of the first inoculation were observed in the pigs that had not previously been inoculated and in the pigs treated with enrofloxacin. Acute phase responses were not recorded in the other three groups, where the pigs had seroconverted to A pleuropneumoniae serotype 2 following the first inoculation.

C-reactive protein quantification in porcine saliva: a minimally invasive test for pig health monitoring

Study objectives were to investigate whether C-reactive protein (CRP) in pig saliva could be quantified using an adapted, time-resolved immunofluorometry assay (TR-IFMA), and to determine whether the assay could distinguish healthy from diseased animals. The test method had intra- and inter-assay coefficients of variation of 5.75% and 9.73%, respectively, the limit of detection was 0.47ng/mL and the coefficient of determination was 0.98. Analysis of CRP concentrations in paired serum and saliva samples from 50 pigs gave a positive correlation (r=0.702, P<0.01) and the salivary CRP concentration was able to distinguish healthy from diseased animals in 62 samples from pigs with naturally occurring or experimentally-induced inflammation. The results suggest that this minimally invasive, straightforward and sensitive assay may be useful in pig health and welfare monitoring.

Age-dependent changes of proinflammatory cytokine production by porcine peripheral blood phagocytes

The aim of the present study was to determine postnatal ontogeny of proinflammatory cytokines IL-1beta, IL-8 and TNF-alpha production by in vitro stimulated porcine blood leukocytes. Four age categories of pigs were chosen. Cytokine production was determined using intracellular flow cytometry. It was found that IL-8 and TNF-alpha production by blood monocytes significantly increased during the postnatal period while production of IL-1beta remained unchanged. In blood neutrophils, the IL-8 production increased only during the postnatal period, while the levels of TNF-alpha and IL-1beta were undetectable during the whole postnatal period. Generally, the most intensive changes in cytokine production occurred before weaning. The production of low levels of cytokines by monocytes and neutrophils from young pigs was not caused by a delayed cytokine response because the cytokine production after 8-h stimulation was lower than that after 4-h stimulation in all age categories. The ontogenetical changes showed the same trends when two different stimulators (LPS, heat-inactivated E. coli) were used, suggesting that the ontogenetical changes are not caused by a simple defect in one signalling pathway, but it is probably a more complex process. No differences in cytokine production between the whole blood and the isolated cells supplemented with newborn or adult serum were found. Thus the ability of newborn monocytes and neutrophils to produce proinflammatory cytokines was not decreased due to the influence of composition of the microenvironment, where the cells were present. In conclusion, the ability of porcine blood leukocytes to produce cytokines develops during postnatal life.