PDE6B and pulmonary tuberculosis: Consequently, we reasoned that in an attempt to find surrogate markers of the effect of LTBI therapy, it would be important to determine in a prospective study whether, in a defined population of recent healthy close contacts of patients with pulmonary TB, isoniazid (INH) for LTBI treatment could cause changes in MTB-specific immune responses to a variety of RD1 antigens, such as the RD1 overlapping peptides of the QuantiFERON TB-Gold assay (QTF-G), RD1 intact proteins and selected peptides.