I hear that some Eurasians – probably more than some – have Neanderthal or Denisovan versions of TLRs. Not surprising: we’ve already seen this happen with other immune system genes – HLA variants , OAS1, STAT2 all have adaptive variants that originated with archaic humans.
TLRs (Toll-Like Receptors) are just plain interesting, but I don’t think many people are familiar with them. They’re part of the innate immune system: they don’t learn from experience, as happens with the adaptive immune system (recombination, clonal selection and all that): they just know. Born that way.
They sense pathogens by detecting molecular patterns characteristic of major classes of pathogens that we just don’t have. These are called PAMPs (pathogen-associated molecular patterns). They can detect lipopolysaccharide (LPS), characteristic of gram-negative bacteria. and peptidoglycan, characteristic of gram-positive bacteria. Some detect viral-double-stranded RNA.
There are ten TLRs in humans. Generally, they react with molecular patterns that we don’t even have. TLR-1 recognizes bacterial lipoprotein and peptidoglycans (strep and staph), TLR-2 recognizes bacterial peptidoglycans( gram-positive bacteria) and zymosan (fungi), TLR-3 double stranded RNA (viruses) , TLR-4 lipopolysaccharides (salmonella) , TLR-5 bacterial flagella (listeria) , TLR-6 bacterial lipoprotein, TLR-7 single-stranded RNA (viruses) , TLR-8 single-stranded RNA(viruses) , TLR-9 CpG DNA (bacteria) . TLR-10 appears to play an inhibitory role, down-regulating TLR-2 .
Back in the days when vaccine development was cutting-edge, I think that people knew that the body automatically reacted to some pathogens, but it has taken a long time to discover the complex details, not that we’re quite done yet.
P.S. according to some, one factor inducing Pygmyization was the high pathogen load in dense tropical jungles. I don’t know if that was the case, but if so, considering that it looks as if African Pygmies (also Bushmen) admixed a bit with a very divergent hominid population (more divergent than Neanderthals) , it wouldn’t be surprising if they picked up some immune system gene variants that helped deal with that jungle environment.