Galectin-1 modulation of neutrophil reactive oxygen species production depends on the cell activation state

Here we report the effects of exogenous and endogenous galectin-1 (Gal-1) in modulating the functional responses of human and murine neutrophils at different stages of activation, i.e. naive, primed, and activated. Exposure to Gal-1 did not induce ROS production in either naive or N-formyl-methionyl-leucyl-phenylalanineprimed (fMLP; 10-9 M) neutrophils. However, Gal-1 elicited a concentration-dependent ROS production in neutrophils activated with fMLP at concentrations ranging from 10'8 M to 10'6 M. Additional fMLP (10'7 M) stimulation of fMLP-activated neutrophils increased ROS production, whose intensity was inversely related to the fMLP concentration used in the first activation step (10-8 M to 10(-6) M), and was not influenced by the presence of Gal(-1). Naive neutrophils treated with Gal-1 and then exposed to fMLP (10(-6) M) or phorbol-12myristate-13-acetate M) produced less ROS, as compared to naive neutrophils not treated with Gal-1. Interestingly, these in vitro Gal-1 effects were associated with Gal-1 carbohydrate-binding activity and the ability to decrease FPR-1 (formyl peptide receptor 1) expression in naive human neutrophils. Conversely, positive ROS modulation by Gal(-1) in activated neutrophils was not associated with FPR-1 expression but it was related to its carbohydrate recognition. In vitro, fMLP stimulation of Gal-1(-/)- mouse neutrophils produced more ROS than fMLP stimulation of Gal-1 (+/+) neutrophils and this effect may be associated with increased FPR-1 expression. Exogenous Gal-i induced ROS production in Gal-1(+) mouse neutrophils more effectively than in Gal-1(+)1(+) mouse neutrophils. Compared to Gal-1(+/+) mice, Gal-1(+) mice exhibited lower bacterial load in the peritoneal fluid and peripheral blood, thus indicating a greater bactericidal activity in vivo. These findings demonstrate that endogenous Gal-1 restricts ROS generation that correlates with bacterial killing capacity in inflammatory neutrophils. Thus, endogenous and exogenous Gal-1 may either positively or negatively modulate the effector functions of neutrophils according to the cell activation stage.