Dec 17, 2010 09:26 GMT  ·  By

Scientists always wondered why humans are more susceptible to certain infectious diseases, than their primate cousins, and now a new study conducted by the University of Chicago, concluded that the explanation lies in the species-specific changes in immune signaling pathways.

The researchers carried out the first genome-wide, functional comparison of genes regulated by the innate immune system in three primate species – humans, chimpanzees and rhesus macaques, and found possible mediators of differences in disease susceptibility among them.

Luis Barreiro from the Department of Human Genetics, University of Chicago, Illinois, and colleagues, stimulated immune cells from these three primate species, in order to test the functional differences in their immune pathways.

They discovered that the main response, necessary to fight all invading pathogens, has been evolutionarily conserved, and had similar gene expression patterns in all three species.

The differences were in the regulatory response linked with genes involved in fighting certain viral and microbial infections.

The effects were unique for each species, and the researchers speculated that this could be due to the rapid adaptation cycles between specific hosts and viruses.

Between humans and their close primate relatives, the team found many changes in immune system genes.

Genomic comparisons showed, for example, that humans were more sensitive than chimpanzees to the severe effects of certain viral infections, like the progression of HIV to AIDS or severe complications from hepatitis B.

Chimpanzees had many HIV-interacting genes that did not respond in the other two primate species, and the team concluded that since these animals do not routinely develop AIDS after HIV/SIV infection, this could be part of a mechanism of chimpanzee resistance to the virus.

Humans had very rich immune responses for genes known to be involved in apoptosis – cell death, and cancer biology.

The authors said that this research is “only the first step in characterizing inter-species differences in immune response” and that more experiments are necessary to evaluate the phenotypic impact of the observed species-specific immune responses.

Also, future research will test the immune response of each species to specific infectious agents.

These results of the study are published in the open-access journal PLoS Genetics.