sentences:  All affected were found to have a functional defect in the upregulation of TNFα production by their blood macrophages in response to stimulation with IFNγ.Furthermore, all lacked expression of IFNγR's on their blood monocytes or lymphocytes, and each was found to have a mutation in the gene on chromosome 6q22-q23 that encodes IFNγR1.Of interest, these children did not appear to be susceptible to infection with agents other than mycobacteria.