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Biomedical subjects

M F Lima

Publications and source records attributed to M F Lima.

28 records · Page 2Linked to original sources
PubMed1987

Lactoferrin effects of phagocytic cell function. II. The presence of iron is required for the lactoferrin molecule to stimulate intracellular killing by macrophages but not to enhance the uptake of particles and microorganisms.

Human lactoferrin (LF)--a neutrophil glycoprotein, the body fluid levels of which increase in inflammatory conditions--stimulates the phagocytic and cytotoxic properties of macrophages. We found in this work that, whereas the presence of iron in the LF molecule was not required to increase the capacity of mouse peritoneal macrophages (MPM) to take up Trypanosoma cruzi amastigotes (AMA), Listeria monocytogenes, or latex particles, it was necessary for LF to enhance intracellular killing of the two microorganisms. Thus, iron-free human lactoferrin (ApoLF), which did not increase MPM cytotoxicity, after restoration of ferric ions prior to its use in MPM treatments or when ferric citrate was added to the culture medium immediately after ApoLF treatment of the MPM, does increase MPM cytotoxicity. In that iron ions cannot be internalized as such, the latter observation suggested that ApoLF had taken up iron while membrane bound and then enhanced killing. Immunofluorescence studies revealed that comparable proportions of MPM-bound ApoLF or LF at either 20 or 100% iron saturation without appreciable differences in fluorescence intensity. Therefore, reduced binding of ApoLF compared with LF was not a likely explanation for the lack of effect of ApoLF on MPM killing. LF did not enhance AMA killing by MPM in the presence of the iron chelator deferoxamine. Diethylaminetriamine-pentaacetic acid, an iron chelator which is not incorporated into cells, had a similar effect. The iron-binding protein transferrin did not alter the capacity of MPM to either take up or kill the AMA, indicating that the noted LF effects were not shared by all iron-binding proteins. However, prior treatment of MPM with transferrin enabled the cells to display a greater parasite killing capacity after ApoLF treatment, suggesting a role for iron in this activity. Whether iron is required for LF to impart the signal that elicits enhanced killing, to satisfy a biochemical requirement for more effective killing, or both, remains to be clarified. We also found that killing of internalized AMA by LF-treated MPM--previously reported to be mediated in part by H2O2, O2-., and 1O2--was inhibitable by scavengers of OH., and therefore, appears to involve this oxygen metabolite as well.

Animals↗
PubMed1985

Lactoferrin effects on phagocytic cell function. I. Increased uptake and killing of an intracellular parasite by murine macrophages and human monocytes.

Mouse peritoneal macrophages (MPM) or human blood monocytes (HBM) co-cultured with intracellular (amastigote; AMA) forms of Trypanosoma cruzi in the presence of human lactoferrin (LF) took up greater numbers of organisms than in the absence of LF; the proportion of phagocytes taking up AMA was also significantly increased. Pretreatment of either MPM or AMA with LF also enhanced cell-parasite association. By immunofluorescence, HBM, MPM, and AMA were found to bind LF. By using 125I-labeled LF, each AMA was determined to have an average 1.1 X 10(6) surface receptors for LF. The enhancing effect of LF on cell-parasite association was inhibited when either rabbit anti-LF IgG or alpha-methyl mannoside (alpha-MM) was present during the incubation of MPM or AMA with LF, or when AMA pretreated with LF were then incubated with either of the LF blocking agents. Although these findings seemed to suggest that LF increased MPM-AMA association by bridging these cells, the LF effect was not inhibited when MPM pretreated with LF were subsequently incubated with either alpha-MM or anti-LF. Furthermore, LF stimulated phagocytosis, as denoted by a significant increase in latex particle uptake after LF treatment of MPM. The intracellular killing capacity of HBM or MPM was also stimulated by LF and was denoted by increased AMA destruction after LF treatments. The possibility that LF only appeared to increase the rate of AMA killing by simply promoting the engulfment of greater numbers of AMA that would then be destroyed intracellularly seemed unlikely because untreated MPM that had already taken up untreated AMA killed greater numbers of AMA when they were subsequently incubated with LF. The results of experiments with scavengers of oxygen reduction intermediates and of nitroblue tetrazolium reduction tests indicated that H2O2, O2- and 1O2 were involved in the killing of AMA by LF-treated MPM. These results suggest that LF, a glycoprotein secreted by neutrophils in greater than normal amounts during inflammation, may contribute to macrophage clearance of AMA released from infected host cells.

Animals↗
PubMed1984

Effects of treatment of trypomastigote forms of Trypanosoma cruzi or host cells with ethidium bromide on cell infection and intracellular fate of the parasite.

The effects of treatment of virulent blood forms of Trypanosoma cruzi with ethidium bromide (EtBr)-an intercalating drug that inhibits DNA synthesis-on parasite association with (a term to mean surface binding plus internalization) and multiplication within different types of host cells were investigated. EtBr markedly reduced the extent of T. cruzi association with Vero cells or rat heart myoblasts (RHM) as evidenced by significant decreases in both the number of flagellates per cell and the percentage of infected cells with respect to control values obtained with organisms treated with medium alone. In contrast, treatment of Vero cells with EtBr had no significant consequence on the extent of cell-T. cruzi association and did not affect the capacity of the parasites to transform into amastigotes and multiply intracellularly. Very few organisms were able to gain access to the cytoplasms of the host cells after treated with 1 X 10(-5) M EtBr but these were virtually unable to multiply intracellularly. Parasites treated with 1 X 10(-6) M EtBr multiplied at a slower rate than medium-treated organisms. Unlike untreated trypomastigotes, parasites treated with 1 X 10(-5) M EtBr were unable to transform into amastigotes in a cell-free medium that supported the growth of untreated organisms. A marked reduction in the rate of amastigote multiplication was seen in cells with an established infection when they were treated with EtBr. These results suggest that ongoing DNA synthesis by T. cruzi is required for it to effectively bind and infect host cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Susceptibility of insect-borne, metacyclic forms of Trypanosoma cruzi to antibody-mediated mechanisms of destruction.

The effect of passive antibody transfer against infection with vector-borne, metacylic forms of Trypanosoma cruzi, and possible mechanisms of immunologic lysis of these organisms, were examined in this work. Anti-T. cruzi antibodies from mice surviving an infection conferred marked protection against challenge with a lethal dose (2,000 organisms) of metacyclic flagellates isolated from the reduviid insect Rhodnius prolixus. In vitro lysis of these parasites by immune sera from mice or chronic chagasic patients was found to require complement (C) activity since the phenomenon was abrogated by heating the sera at 56 degrees C, adding the C inactivator cobra venom factor or in the absence of divalent cations. The lytic activity was provided via the alternative pathway of C activation since it was readily demonstrable in the absence of calcium ions. The metacyclic trypanosomes were also killed by human lymphocytes, neutrophils and eosinophils in the presence of anti-T. cruzi antibodies. Minimal or insignificant cytotoxicity was afforded by the cells or the antibodies when tested separately. These results emphasize the beneficial role of the humoral immune response in host defense against challenge with the form of T. cruzi responsible for natural infections.

Animals↗
PubMed1982

Biochemical requirements for intracellular invasion by Trypanosoma cruzi: protein synthesis.

The effects of irreversible inhibition of protein synthesis by pactamycin in either infective forms of Trypanosoma cruzi or mammalian host cells on cellular invasion by this human pathogen were investigated. Treatment of bloodstream forms of T. cruzi with pactamycin markedly reduced their ability to bind either fibroblast-like cells of monkey origin or myoblasts of rat origin. The number of amastigote forms that could be established intracellularly was also significantly decreased with respect to control values obtained when mock-treated (medium alone) trypomastigotes were incubated with the cells. Pactamycin treatment also reduced the infectivity of T. cruzi trypomastigotes for mice as evidenced by both significantly reduced parasitemia levels and mortality rates when compared with those of control mice infected with mock-treated parasites. Inhibition of protein synthesis in the host cells neither prevented cell infection by untreated trypomastigotes nor altered the percentages of infected cells or the magnitude of the infection in vitro. These results indicate that protein synthesis is a requirement for cell invasion by T. cruzi and that the parasite can establish itself and replicate within cells relying on its own protein synthesis ability.

Animals↗
PubMedDate not supplied

The ACTH test in the diagnosis of hirsutism.

The ACTH test has been used to confirm the diagnosis of adrenal insufficiency and the classic and the non-classic adrenal hyperplasia due to the 3-HSD, 21 OH e 110H deficiencies. This article reviews the historical aspects of the use of ACTH in the diagnosis of hirsutism and points out its mains indications. In spite of new biological molecular advances in the diagnosis of adrenal enzymatic deficiencies, the use of the ACTH test can help the physician to predict both genothipus and fenothipus in populations with hyperandrogenic manifestations due to non-classical or late-onset congenital adrenal hyperplasia.

Adrenocorticotropic Hormone↗