Interestingly, TLR4-induced monocyte expression of IFN-α and TLR4/TLR-7/8/9–induced expression of MIP-1β was decreased in PTD cases in initiators, suggesting that the reduced immune activation may be indicative of reduced responsiveness to antigen stimulation (immune senescence) as an underlying mechanism. This evidence concerns the gene TLR4 and Bjornstad syndrome.