C1 Apicomplexan parasite load and immune responses in the cheetah (Wachter)
|Research Group:||Department Evolutionary Ecology
Leibniz Institute for Zoo and Wildlife Research (IZW)
|Address:||Alfred-Kowalke-Str. 17, 10315 Berlin|
|Supervisors:||Dr. Bettina Wachter|
|Doctoral Researcher:||Maria Serocki|
State of the art:
In natural environments, both hosts and parasites are under selection pressure. Threatened
free-ranging wildlife populations might be particularly susceptible to parasites, especially if their
immune system is impaired. Cheetahs exhibit low diversity at the MHC, important fitnessrelated
immune genes that are part of the adaptive immune system. Cheetahs compensate
for this impairment in their adaptive immunity at least in part with a strong constitutive innate
immunity in the humoral immune branch. A key question is therefore how the cheetah
immune system responds throughout its life-history to apicomplexan parasite infections, ticks
and co-infections, and what functionality immune cells have.
Previous own work:
During an ongoing, long-term (16 years) study we collected blood and faecal samples from
~300 free-ranging cheetahs and ~80 free-ranging leopards in Namibia. We fitted adult animals
with GPS collars and know their age, reproductive status and whether males are territory
holders. We adapted and validated numerous protocols for cheetahs and leopards to
measure functional immune responses and inflammatory and anti-inflammatory cytokines, and
currently develop a protocol to measure blood cell ratios with flow cytometry. We demonstrated
that cheetahs have a higher humoral constitutive innate immunity but a lower induced innate
and adaptive immunity than leopards, which have a high diversity at the MHC. We
further screened serum samples for antibodies against several apicomplexan parasites and
investigated faecal samples for gastrointestinal endoparasites. Most cheetahs had antibodies
against Toxoplasma gondii (60%) and shed eggs from Ancylostoma spp. (82%). In close
collaboration with scientists from projects A5 and C5 we recently demonstrated a high
prevalence of five hemoparasites in cheetahs and leopards, including a high frequency of coinfections
(9.6% cheetahs positive for all pathogens).
Hypotheses and work plan:
1) Cheetahs are expected to invest more in MHC-independent and less in MHC-dependent
cellular immunity than leopards.
2) Cheetah immune cells are expected to be less functional when stimulated in vitro than
leopard immune cells.
3) During co-infection, immune response patterns differ from singular infections.
4) Costly life states such as pregnancy, lactation and territory defense are expected to be in a
trade-off with the immune potential of an individual. We therefore expect such individuals to be
infected more often with multiple parasites and to have lower levels of the energetically costly
inflammatory cytokines than non-reproducing females and non-territorial males.
To investigate MHC-independent and MHC-dependent immunity, we will conduct blood cell
counts and flow cytometry. The reactivity of lymphocytes towards mitogens (ConA, LPS) and
parasite-specific antigens will be tested in lymphocyte proliferation assays. We will compare
the immune responses of individuals being infected with one parasite to those of individuals
infected with several parasites.