From tolerance to autoimmunity: is there a risk in early life vaccination?

The potential for vaccines to act as triggers of autoimmune reactions has received much recent attention. Such an association is very poorly defined mechanistically, but may potentially involve epitope mimicry between vaccinal and self antigen, or the immuno-stimulatory effects of vaccine adjuvant. If such reactions occur, they are more likely to involve adults than infants in early life, as a reflection of the immunological immaturity of the newborn. There has been a recent focus in immunology on the link between innate and adaptive immunity provided by dendritic cells and the range of Toll-like receptors (TLRs) that are the point of first contact of these cells with microbial antigen. These interactions appear to determine the nature of the subsequent adaptive immune response and whether it may be mediated by Th1, Th2, Th17 or T regulatory populations. TLR interactions may also be significant in the induction of vaccinal immunity and agonists of these receptors are being developed as potential vaccine adjuvants. There are differences in cytokine production of adult and newborn dendritic cells, and these differences must be considered in the application of such novel adjuvants to products intended for either age group.