Rosette-increasing factor (RIF) generated in vivo following PHA skin test.

In phytohaemagglutinin (PHA) skin test-positive individuals, rosette-increasing factor (RIF), which augmented active E and EA rosette formation, appeared in the serum following the PHA skin testing. This factor was detectable 6 hr after the application of PHA and reached a peak at 14 hr. The appearance of the factor was closely related to the delayed cutaneous hypersensitivity. When mononuclear (MN) cells derived from individuals exhibiting delayed cutaneous reaction were further cultured without the addition of PHA, a similar property was found in the supernatants. Fractionation of the cells by E rosetting revealed this factor to be the product of T lymphocytes. Moreover, despite a lower percentage in contaminated T lymphocytes, a higher RIF activity was observed in the supernatants of the nylon-wool-retained population. The production of RIF was completely inhibited by cytochalasin B, but was not affected by colchicine. Experiments utilizing cycloheximide revealed that new protein synthesis was only necessary for early activation steps. RIF is a kind of lymphokine synthesized in the active immune process in vivo. Therefore, to assay RIF in vivo may provide a new method for investigating the cellular immune competence of the given patients.