Immune reactions to different doses of Eimeria Acervulina in day-old broilers.
W.J.C Swinkels, W.A. Boersma,
JMJ Rebel.
ASG Lelystad p.o. box 65 8200AB Lelystad, The Netherlands. E-mail: willem.swinkels@wur.nl
T-cell responses are the dominant
immune reaction in broilers infected with Eimeria. Different factors that may
influence the kind of T-cell responses to an Eimeria infection are e.g., species
of Eimeria, age of the host, amount of parasite, infection history. In young
chicks, the intestine is still developing. This process means not only an
increase in length, but also that lymphocyte population in the gut develops and
differentiates. In chicks infected at young age, the immune response may be
different in quality as compared to the response in chicks in which the gut is
fully developed. We investigated the (T-cell) immune responses of young broilers
to a primary E. acervulina infection in relation to the number of parasites used
for infection.
In our experiment, we infected day-old broilers with a low (500 oocysts) and a
high (50,000 oocysts) dose of E.acervulina. We used a species-specific real-time
PCR to quantify total amount of parasites in the intestine as the number of
oocysts in faeces may not be representative for the exposure of the gut immune
system. We characterized T-cell subsets in the duodenum by means of fluorescence
antibody cell sorting (FACS), performed lymphocyte proliferation assays with
spleen lymphocytes with E. acervulina antigens, and characterized the mRNA
profiles of different cytokines (TGF-beta2, 4, IFN-gamma, IL2, 6, 8 and 18) in
the duodenum by means of real-time PCR.
From day 5 p.i., broilers infected with a high dose of E.acervulina had
significantly lower body weight than the control group. There was no increase in
CD4+ T-cells, but a strong increase in CD8+ T-cells in the duodenum at day 7 and
9 p.i. was observed in broilers infected with a high dose E. acervulina at one
day of age. Strong IL8 and IL18 mRNA responses were observed after infection
with both doses, but no IFN-gamma and TGF-beta mRNA responses were found in the
duodenum. The specific proliferative T-cell responses to a low infectious dose
were not significantly different as compared to the control group. In conclusion,
based on the kinetics of observed phenomena, a primary infection with a high
dose of E. acervulina in day-old broilers seems to generate an immune response
that shows a peak at the time of oocyst excretion, whereas the immune response
to a low dose is less explicit.