Background: Natural killer (NK) cells, a type of white blood cells, is implicated in many autoimmune diseases, but evidence in MS and its animal models remains uncertain. In an effort to illuminate this, these investigators analysed expression of a NK cell marker, NCR1 (natural cytotoxicity triggering receptor; NKp46; CD335), an activating receptor expressed by virtually all NK cells and therefore considered a pan-marker for NK cells.
Results: They first investigated the expression of NCR1 on peripheral blood white cells and found no significant difference between healthy controls and MS’ers. They then investigated levels in central nervous system (CNS) tissue from MS’ers by detecting mRNA NCR1 transcripts (this is not protein but messenger RNA); levels were increased more than 5 times in active disease lesions. However when they looked under a microscope, very few NCR1+ NK cells were identified. Rather, the major part of NCR1 expression was localised to astrocytes (glial cell), and was considerably more pronounced in MS’ers than controls.
Conclusions: The data presented here show very limited expression of NCR1+ NK cells in MS lesions, the majority of NCR1 expression being accounted for by expression on astrocytes. This is compatible with a role of this cell-type and NCR1 ligand/receptor interactions in the innate immune response in the CNS in MS’ers. An innate immune response refers to hard-wired immunity rather than memory responses. This is the first report of NCR1 expression on astrocytes in MS tissue: it will now be important to unravel the nature of cellular interactions and signalling mediated through innate receptor expression on astrocytes.
“This is another paper that has shown upregulation of the innate immune response in the brains of MS’ers. The innate immune response is a primitive response and is switched on by many stimuli, in particular viruses. I wonder if this is another piece of the viral hypothesis jigsaw? Watch this space!”