In my chapter LESS IS MORE I write at length about the work of Ajit Varki and his group at UC San Diego on the evolution of what they see as the highly aberrant human immune system - compared, at least, with the other great apes and primates. The idea is that the human immune system has been primed to be over-reactive to invading foreign proteins - antigens encountered from a host of new or rapidly evolving parasites and micro-organisms. Here they expand on the work I have already reported by looking further at the role of Siglec-5 immuno-globulins on the cell surface of human T and B cells. Today, we see this over-reactivity in a range of debilitating auto-immune diseases we do not share with chimps. Fascinating stuff! Here's the conclusion of their abstract - which will make sense if you've read the book!!
"Finally, we show a relative increase in activation markers and cytokine production in human lymphocytes in response to uridine-rich (viral-like) ssRNA. Thus, humans manifest a generalized lymphocyte over-reactivity relative to chimpanzees, a finding that is correlated with decreased levels of inhibitory sialic acid-recognizing Ig-superfamily lectins (Siglecs; particularly Siglec-5) on human T and B cells. Furthermore, Siglec-5 levels are upregulated by activation in chimpanzee but not human lymphocytes, and human T cell reactivity can be downmodulated by forced expression of Siglec-5. Thus, a key difference in the immune reactivity of chimp and human lymphocytes appears to be related to the differential expression of Siglec-5. Taken together, these data may help explain human propensities for diseases associated with excessive activation of the adaptive immune system."
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