Use of the CTL44 cell line, a derivative of CTL/L cells, to identify and quantify mouse interleukin-4 by bioassay

The isolation and characterization of a new and excellent indicator cell line for murine interleukin-4 (IL-4) bioassays, CTL44, is described. CTL44, a subline of CTL/L cells, is vigorously responsive to murine IL-4, but hyporesponsive to IL-2, requiring > 6 ng/ml (approximately 120 U/ml) of human IL-2 or > 80 U/ml of mouse IL-2 to induce IL-2 dependent proliferation. In CTL44 both IL-4 receptor mRNA accumulation and cell surface expression are detected, whereas IL-2 receptor expression appears to be absent. CTL44 cells maintained in IL-4 containing medium grow rapidly in a non-adherent fashion, and can be stored frozen in liquid nitrogen without loss of function.