Free-ranging cheetahs are in good health although they come into contact with a large variety of pathogens, as outlined in sub-project on health status. This is interesting because cheetahs have a low genetic variability at the level of e.g. microsatellites and mitochondrial DNA. To better understand the relationship between the genetic variability and health/immunity, we investigated the Major Histocompatibility Complex (MHC) of cheetahs, a polymorphic gene group in vertebrates that is essential for the adaptive immune system. Together with our collaborators, we detected ten different MHC class I alleles and four MHC class II alleles. This relatively low MHC diversity is likely linked to a low adaptive immunity, but does not appear to hamper the good immunocompetence of cheetahs. This raises the question whether the innate immune system, which is not linked that tightly to the MHC as the adaptive immune system, is particularly potent and can compensate for the low potential of the adaptive immune system.
We measured with our collaborators the potential of the innate immunity of cheetahs with a bacteria killing assay. For this we challenged in the laboratory the blood of cheetahs with the bacteria Escherichia coli. For comparison, we did the same with blood of five other carnivore species. Our results revealed that cheetahs mounted the strongest innate immune response against the bacteria compared to leopards, lions, caracals, brown hyenas and jackals. We conducted five additional immune tests with cheetahs and leopards, which have a higher MHC variability than cheetahs. We looked deeper into the innate immune system which can be further divided into the constitutive and induced parts. Cheetahs had a higher potential of the constitutive innate immune system, while leopards had a higher potential of the induced innate and adaptive immune systems. This suggests that cheetahs compensate for their low MHC immune potential with a strong constitutive innate immune system, which can explain their good health in the wild.
We further investigated the oxidative stress levels in cheetahs and leopards. Glucocorticoid levels give a useful information on general allostatic load (“stress”) levels of individuals, see sub-project on reproduction and endocrinology. But these stress hormones do not provide an indication of the molecular oxidative damage cause by free radicals that might be induced by excessive stress exposure. Oxidative stress can cause cellular damage or suppress the immune system. Together with our collaborators we measured oxidative stress within cheetahs and also between cheetahs and leopards. We found that cheetah females had higher levels of oxidative stress than cheetah males, leopard females and leopard males. This might be due to the high cost for cheetah females of raising up to six cubs in a litter, which is more than the one or two cubs of leopard females.
Publications reporting on these topics
Castro-Prieto A, Wachter B, Melzheimer J, Thalwitzer S, Sommer S 2011: Diversity and evolutionary patterns of immune genes in free-ranging Namibian leopards (Panthera pardus pardus). Journal of Heredity 102: 653-665. Doi: 10.1093/jhered/esr097.
Castro-Prieto A, Wachter B, Sommer S 2011: Cheetah paradigm revisited: MHC diversity in the world’s largest free-ranging population. Molecular Biology and Evolution 28: 1455-1468. Doi: 10.1093/molbev/msq330.
Castro-Prieto A, Wachter B, Melzheimer J, Thalwitzer S, Hofer H, Sommer S 2012: Immunogenetic variation and differential pathogen exposure in free-ranging cheetahs across Namibian farmlands. PLoS ONE 7(11): e49129. Doi: 10.1371/journal.pone.0049129.
Heinrich SK, Wachter B, Aschenborn OHK, Thalwitzer S, Melzheimer J, Hofer H, Czirják GÁ 2016: Feliform carnivores have a distinguished constitutive innate immune response. Biology Open 5: 550-555. Doi: 10.1242/bio.014902.
Costantini D, Wachter B, Melzheimer J, Czirják GÁ 2017: Socioecological and environmental predictors of physiological stress markers in a threatened feline species. Conservation Physiology 5(1). Doi: 10.1093/conphys/cox069.
Heinrich SK, Hofer H, Courtiol A, Melzheimer J, Dehnhard M, Czirják GÁ, Wachter B 2017: Cheetahs have a stronger constitutive innate immunity than leopards. Scientific Reports 7:44837. Doi: 10.1038/srep44837.
Costantini D, Czirják GÁ, Melzheimer J, Menges V, Wachter B 2018: Sex and species differences of stress markers in sympatric cheetahs and leopards in Namibia. Comparative Biochemistry and Physiology, Part A 227: 8-13. Doi: 10.1016/j.cbpa.2018.09.002.
Schwensow N, Castro-Prieto A, Wachter B, Sommer S 2019: Immunological MHC supertypes and allelic expression: how low is the functional MHC diversity in free-ranging Namibian cheetahs? Conservation Genetics. Doi: 10.1007/s10592-019-01143-x.