However, the in vivo role of B cell IL-4 per se was unclear, with studies showing that it was required for Th2 responses with resultant worsening of leishmaniasis, but it was not required for Th2 responses and protection from helminthic infections or pulmonary/airway inflammation in allergic asthma (7, 20–22). This evidence concerns the gene IL4 and allergic asthma.