Do porins inhibit the macrophage phagocyting activity by stimulating the adenylate cyclase? 
Porins interact with macrophage membranes and inhibit their phagocyting activity.  We have tested the porin effect on a biologically relevant membrane-bound enzymic activity, the adenylate cyclase system, which appears to be stimulated both in the presence of Mn2+ and Mg2+ or Mg2+ + Gpp(NH)p.  Moreover, for mice macrophages incubated in the presence of porins, there is an increase in the intracellular cAMP content after 5 min of incubation, with a maximum after 15 min of incubation.  The results shown suggest that the porin effects on the adenylate cyclase can represent the molecular basis of the porin-dependent inhibition of the macrophages phagocytosis.  Our point of view, which proposes a cAMP role in inhibiting the phagocyting activity in macrophages, is supported also by the results of the experiments carried out in the presence of both dibutyryl-cAMP or aminophylline.  The phagocyting activity is inhibited in all cases and independently of the bacteria to be phagocyted.