Trying to Explain a Paradox

One question that keeps coming up at the meeting here is the paradox that compared with developed countries, some oral vaccines are less efficient in malnourished children in developing countries, even though such children show an overstimulation of their immune system in the gut. 

A possible explanation was mentioned today by Per Brandtzaeg of the University of Oslo who gave an overview of the human intestinal immune system. He said that malnourished children in developing countries may have too many regulatory T cells (Tregs), which may explain why their immune response to oral vaccines is suppressed.   

Hints that this might be the case come from observations that parasitic infections can result in an excess number of Tregs. For example, Brandtzaeg mentioned a study that described case of a patient who had a parasite infestation which resulted in a large number of Tregs. When the parasitic infestation was treated, the parasites went away, but the numbers of the patient’s Tregs went down to very few and the patient developed inflammatory bowel disease.

This suggests that the Tregs induced by the parasite kept the inflammatory bowel disease under control, Brandtzaeg said. If there is a similar expansion of Tregs in the gut of malnourished children in developing countries, “it could actually dampen the immune system to an extent that they don’t get a good response to oral vaccines,” he said.

However, nobody knows if this is the case because nobody has studied the number of regulatory T cells in such children. “No one has really looked at regulatory T cells in the developing world,” he said. “Why don’t people study if there is an expansion of regulatory T cells in the gut of these developing country children?"