[W]e have estimated that natural selection drives twice as much change in immune-related proteins as in proteins with no immune function. Interestingly, the rate of adaptation is also more variable among immunity genes than among other genes in the genome, with a small subset of immunity genes evolving under intense natural selection. We suggest that these genes may represent hotspots of host–parasite coevolution within the genome.
–Obbard, D., Welch, J., Kim, K., & Jiggins, F. (2009). Quantifying Adaptive Evolution in the Drosophila Immune System PLoS Genetics, 5 (10) DOI: 10.1371/journal.pgen.1000698
(This is particularly interesting to me because I’m trying to look at co-evolution between pathogens and immunity myself. I’ve been tentatively suggesting that adaptive immune components (co)-evolve faster than innate immune components; of course, Drosophila only have innate immunity, so this paper suggests that the innate immune system also evolves rapidly. That’s not unexpected, and doesn’t disprove my hypothesis, but it’s interesting anyway. Also, there are some techniques in here I might be able to make use of.)
In hindsight it seems pretty natural that the part of the genome that deals with the most fluent part of the environment (the pathogenic organisms that themselves evolve fast) is under the strongest selective pressure and will adapt quickly, and your suggestion looks like a sensible extrapolation. (All this of course being my gut feeling rather than a product of careful consideration).
Anyway, I hope you’ll be succesful in testing your hypothesis… :)
Wouldn’t you consider the MHC to be part of both innate and adaptive immune system? Natural Killer cell receptors are an example of fast evolving (innate) immune receptors, see for instance the KIR genes in primates or Ly49 genes in mice. Always reading your posts with much interest!
Very interesting thoughts! Immunity to diseases and gene research always sparks my curiousity because I am interested in how we work and always want to be safe in case of dangerous outbreaks (actually just bought masks to protect in the event of a plague or chemical agent attack).