Posted by: Glow-worm PJ27 FEB 2013
Recent research at Stanford University School of Medicine, published in Immunity, has cast doubt on the established view of the immune response, and of acquired immunity, when it was discovered that a class of T-lymphocytes seemed to have developed a memory of microbes they had never encountered.
T-cells respond to markers called epitopes on pathogenic cells, and it was thought that there was a T-cell specific to each of the potentially billions of epitopes in the environment. The T-cells exist in a naive state until challenged by their specific epitope, when they multiply and eventually respond to the pathogenic attack. In the event of future exposure
to the same pathogen, the T-cells are now ready to mount an immediate response, and are said to be in the memory state.
Sophisticated sampling techniques enabled the Stanford team to isolate specific target epitopes from blood samples from both healthy adults and newborn babies. Almost all the adult samples contained cells responsive to HIV, with half of these being in the memory state, despite none of the patients ever having being exposed to HIV.
Furthermore, around one fifth of the memory state cells also responded to other harmless environmental microbes, suggesting that T-cells, rather than being specific, can cross-react to epitopes of similar structure. No T-cells from the newborn sample were in the memory state, and the suggestion is that exposure to non-pathogenic environmental organisms conveys immunity against similar epitopes of other organisms, including deadly pathogens.
It was further discovered that volunteers vaccinated against one virus, for example, influenza, demonstrated reactivity not only to this virus, but to epitopes of several different bacteria, viruses and protozoa. This cross-reactivity could explain observations that the vaccination of African children against measles decreases the overall mortality by more than is attributable to measles alone. It is hoped that more research into the mechanism of cross-reactivity may lead to the development of “wide spectrum” vaccines for use in developing countries.