We show that the response to MABSC in CF follows a pattern seen in other mycobacterial infections, with a Th1-dominated response, characterised by the predominance of CD4 T cells, mainly coordinated by IFN-γ and TNF-α, and a secondary role of B cells, which contrasts with the Th2-skewed response seen in chronic P. aeruginosa infection. The gene discussed is CD4; the disease is cystic fibrosis.