Interestingly, also in TNF−/− mice as well as TNF-R1−/− mice, the increase in Fas expression on both T1 and T2 transitional B-cells preceded the rapid loss of these cells from the spleen further suggesting a correlation between the up-regulation of surface-expressed Fas and the trypanosomiasis-associated destruction of the transitional B-cell compartment (Figure S4). The gene discussed is TNF; the disease is trypanosomiasis.