We next tested a large cohort of BMT mice for CD3 and H2b expression, discovering that in WT mice a significant portion of CD3+ cells did not stain for H2b− following helminth infection but that almost all CD3+ cells from IL-4−/−, STAT6−/−, or IL-4Rα−/− BMT recipients did (Fig. 1). The gene discussed is IL4; the disease is helminthiasis.