8 research outputs found
Adenylate Cyclase Toxin Promotes Internalisation of Integrins and Raft Components and Decreases Macrophage Adhesion Capacity
Bordetella pertussis, the bacterium that causes whooping cough, secretes an adenylate cyclase toxin (ACT) that must be post-translationally palmitoylated in the bacterium cytosol to be active. The toxin targets phagocytes expressing the CD11b/CD18 integrin receptor. It delivers a catalytic adenylate cyclase domain into the target cell cytosol producing a rapid increase of intracellular cAMP concentration that suppresses bactericidal functions of the phagocyte. ACT also induces calcium fluxes into target cells. Biochemical, biophysical and cell biology approaches have been applied here to show evidence that ACT and integrin molecules, along with other raft components, are rapidly internalized by the macrophages in a toxin-induced calcium rise-dependent process. The toxin-triggered internalisation events occur through two different routes of entry, chlorpromazine-sensitive receptor-mediated endocytosis and clathrin-independent internalisation, maybe acting in parallel. ACT locates into raft-like domains, and is internalised, also in cells devoid of receptor. Altogether our results suggest that adenylate cyclase toxin, and maybe other homologous pathogenic toxins from the RTX (Repeats in Toxin) family to which ACT belongs, may be endowed with an intrinsic capacity to, directly and efficiently, insert into raft-like domains, promoting there its multiple activities. One direct consequence of the integrin removal from the cell surface of the macrophages is the hampering of their adhesion ability, a fundamental property in the immune response of the leukocytes that could be instrumental in the pathogenesis of Bordetella pertussis
The use of mtt [3-(4, 5-dimethyl-2-thiazolyl) -2, 5-diphenyl -2h- tetrazolium bromide]-reduction as an indicator of the effects of strain-specific, polyclonal rabbit antisera on Candida albicans and C. krusei
There is only scanty data on the effects of specific antibody, with or
without complement, on Candida albicans or Candida krusei in
cell-free systems in vitro , although previously published work has
shown that specific antibody mediates anti- Candida immunity in vivo
by inhibition of adherence to host cells or surfaces and by the
promotion of phagocytosis and intra-phagocytic killing. The MTT (3-[4,
5-dimethyl-2-thiazolyl] -2, 5-diphenyl -2H- tetrazolium
bromide)-reduction method as a test of the viability of fungi was used
to investigate the effect of complement, normal serum and immune serum
on these two species of Candida that are of increasing importance as
opportunistic pathogens. We report that normal rabbit serum or
strain-specific, polyclonal anti- Candida rabbit antibody, with or
without guinea pig complement, did not cause the reduction of total
cell-mass or of the viability of either C. albicans or C. krusei, in
vitro as determined by the MTT-reduction test. Complement alone without
specific antibody, also, had no such effect on these two Candida
species