J. Lundahl et al., SERUM PROTECTS AGAINST AZUROPHIL GRANULE DEPENDENT DOWN-REGULATION OFCOMPLEMENT-RECEPTOR-TYPE-1 (CR-1) ON HUMAN NEUTROPHILS, Inflammation research, 44(10), 1995, pp. 438-446
We have investigated the effect of gradual degranulation on the expres
sion of functional receptors (CR1 and CR3) on human neutrophils. Incub
ation with increasing concentrations of fMLP (10(-10)-10(-7) M) transl
ocated CR1 and CR3 to the cell surface in a similar kinetic pattern. W
hen reaching maximal expression of receptors (10(-7) M fMLP), 78 +/- 1
0% and 87 +/- 9% of the total pool of CR1 and CR3, respectively, were
translocated to the cell surface. To drive the mobilization process fu
rther, cytochalasin B was introduced to increase the stimulatory effec
t of fMLP. No further increase in CR1 surface expression was obtained.
However, we found a characteristic time course of surface appearance
of CR1 and CR3 with a maximal surface expression within 1 minute, foll
owed by a time-related down-regulation of CR1 but not CR3. In addition
, the total pool of CR1 in cytochalasin B treated neutrophils was redu
ced after 15 minutes stimulation with fMLP measured by how cytometry a
nd immunoblotting, indicating degradation of CR1. The down-regulation
of CR1 was concomitant with a translocation of azurophil granules, in
terms of upregulation of CD63. Azurophil, but not specific nor secreto
ry, granule fractions caused a down-regulation of CR1 on fMLP activate
d neutrophils. The presence of human sera and serine protease inhibito
r protected CR1 from down-regulation, Together, these findings indicat
e that intracellular stored proteases, released in the late part of th
e sequential mobilization process, alters the expression of functional
receptors mobilized in the early part of the mobilization process. Th
e findings also focus on the importance of the microenvironment for th
e net outcome of neutrophil activation in terms of functional receptor
expression.