An anti-Klebsiella pneumoniae K5a capsular polysaccharide vaccine was evaluated as a preventive approach for protecting squirrel monkeys, Saimiri sciureus, in our breeding colony. Based on an 8-month vaccination schedule over a period of more than two years, this vaccine, regardless of the animal's age, resulted in a reduction of this particular bacterial infection and its generally associated fatal outcome. IgG antibody responses in naive and vaccinated animals were monitored over an extended period by radioimmunoassay and showed a marked increase above the initial naturally occurring antibody titres. No side-effects were observed after repeated vaccination of several hundred animals during a two-year period.

Animals↗

PubMedDate not supplied

Peripheral blood mononuclear cells in the squirrel monkey Saimiri sciureus: characterization and functional aspects of T lymphocytes.

Characterization and functional aspects of squirrel monkey peripheral blood mononuclear cells (PBMC), and mainly T cells, are described in the present paper; this should enable the study of cellular immune responses in an experimental model for malaria. PBMC were obtained from Ficoll-Hypaque gradient separation and fractionated into T cells and non-T cells by means of E-rosetting techniques and adherence to plastic dishes. PBMC subset phenotypes were characterized by means of monoclonal antibodies (mAb) directed against human leukocyte differentiation antigens (Ag), fluoresceinated lectins, anti-surface Ig (squirrel-monkey-specific) antibodies (Ab) and latex bead ingestion assays. PBMC functions were assayed through lymphoblastic transformation tests (LTT) in the presence of either numerous mitogenic, comitogenic and anti-mitogenic lectins or anti-human leukocyte differentiation Ag mAb. We sought to standardize reference values for lymphocyte phenotypes and functions in normal squirrel monkeys (prior to experimental infection). We also present evidence that splenectomy (generally rendered necessary for experimental human malaria infection) performed six months prior to the present investigation did not modify PBMC numbers and functions in the tested animals.

Animals↗

PubMedDate not supplied

Opsonization as an effector mechanism in human protection against asexual blood stages of Plasmodium falciparum: functional role of IgG subclasses.

A phagocytic assay performed with human peripheral mononuclear cells and malaria-infected erythrocytes enabled the study of opsonizing antibodies in human serum from donors presenting different levels of protective immunity. Opsonizing activity was found in sera from individuals who could be considered immune, i.e. asymptomatic parasite carriers and subjects residing in endemic regions who presented neither symptoms nor parasites. This contrasted with subjects showing an absence of symptoms or who had experienced only a single malarial infection. All sera contained high levels of antimalarial antibodies, as shown by immunofluorescence assay (IFA). IgG of different subclasses were immunopurified from these sera. All subclasses were shown to bind to the surface of infected erythrocytes by FACS analysis, but only IgG1 and IgG3 were able to mediate opsonization. IgG2 and IgG4 did not opsonize and inhibited the opsonizing activity of IgG1 and IgG3 in competition experiments. These results suggest the existence of a correlation between immune protection, the ability of serum to mediate opsonization of infected erythrocytes and the predominance, in this serum, of IgG1 and IgG3 over IgG2 and IgG4 directed against the surface of the infected erythrocytes.

Animals↗

PubMedDate not supplied

Cloning and expression of genomic DNA sequences coding for putative erythrocyte membrane-associated antigens of Plasmodium falciparum.

Genomic DNA fragments of Plasmodium falciparum generated by mung bean nuclease digestion were cloned in the lambda expression vector lambda JK2. The resulting library was screened with a rabbit antiserum raised against purified membranes of P. falciparum-infected erythrocytes and with a serum pool from immune humans from an endemic area of Liberia. Positive clones were rescreened with a series of human and monkey sera. Twelve selected clones were analysed in detail. Four of them corresponded to already described membrane-associated P. falciparum antigens. The other positive clones contained inserts which, according to the nucleotide sequence, Southern blot analysis and immunological characteristics, correspond to so far unknown antigens.

Amino Acid Sequence↗

PubMedDate not supplied

Peripheral blood mononuclear cells in the squirrel monkey Saimiri sciureus. II. Exploration of the IL2/IL2R pathway of T-cell activation.

We report here on functional aspects of squirrel monkey T cells isolated either from peripheral blood mononuclear cells or in the presence of accessory cells or accessory-cell-secreted cytokines. The T-cell response triggered by polyclonal activators was measured through proliferation, T-cell growth factor production and transient expression of receptors to growth factors. We also sought to delineate mechanisms by which antimitogenic molecules might prevent lymphocytes from being able to express "activation antigens" and/or from proliferating. Under these conditions, we mainly explored the inducible IL2/IL2R pathway and phenomena occurring in lymphocyte "non-activation" in terms of early and late cellular events; indeed, defects in the IL2/IL2R pathway represent one of the dysregulation events presumed to occur during the acute phase of human malaria, disease for which. Saimiri monkeys have been selected as experimental hosts.

Animals↗

PubMedDate not supplied

Chondroitin-4-sulphate (proteoglycan), a receptor for Plasmodium falciparum-infected erythrocyte adherence on brain microvascular endothelial cells.

Adherence of Plasmodium falciparum parasitized erythrocytes to the microvascular endothelium is mediated by different receptors expressed by endothelial cells. The study of the adherence of P. falciparum-infected erythrocytes to Saimiri monkey brain microvascular endothelial cells revealed the presence of an additional receptor, which was identified and further characterized. This receptor was also found on the surface of primary human lung endothelial cells (HLEC). We developed two mAbs to this receptor which very efficiently blocked the adherence of parasite strains to Saimiri brain endothelial cells (SBEC). The ability of these mAb to bind to SBEC was partially blocked by chondroitin-4-sulphate (CSA). Competitive inhibition assays on adherence of parasitized red blood cells (PRBC) showed that CSA, but not hyaluronic acid, chondroitin-6-sulphate, dermatan sulphate, keratane sulphate, heparan sulphate or chondroitin-4S-disaccharide, was able to almost completely inhibit PRBC adherence. The same effect was obtained with chondroitinase ABC and AC, but not B, hyaluronidase or heparinase. These results strongly suggest that a member of the chondroitin-glycosaminoglycan family, CSA, represents an additional receptor used by P. falciparum PRBC to cytoadhere to microvascular endothelial cells.

Animals↗

PubMedDate not supplied

Antibodies from immune African donors with a protective effect in Plasmodium falciparum human infection are also able to control asexual blood forms of the parasite in Saimiri monkeys.

We have recently shown that an IgG preparation obtained from immune African donors was able to control Plasmodium falciparum multiplication in the blood of Thai patients, but had no inhibitory activity against the parasite in vitro. The same IgG preparation was passively transferred to Saimiri monkeys acutely infected with two different strains of P. falciparum, one of African origin and the other from French Guyana. A dose-dependent in vivo inhibition of parasite development was observed with both strains. The results justify the use of Saimiri monkeys for malaria vaccine trials and permit the introduction of new techniques for screening of candidate antigens for vaccines.

Animals↗

PubMedDate not supplied

Characterization by anti-Ig monoclonal antibodies of protective and non-protective antibodies against asexual forms of Plasmodium falciparum in the Saimiri monkey.

Four monoclonal antibodies (mAb) which recognize distinct epitopes on Saimiri immunoglobulins were successfully used to characterize the protective and non-protective antibodies developed by this experimental host in response to infection by the human malaria parasite Plasmodium falciparum. Two of these mAb, 3F11/G10 and 3E4/H8, were IgG-specific and directed against conformationally conserved epitopes on the intact molecule. mAb 3A2/G6 and 4G3/B5 were specific for epitopes on two distinct L chain types of all Ig. Radioimmunoassay and immunoblots indicated that L-chains defined by 3A2/G6 were present in IgG molecules of type 3F11/G10, while L chains defined by 4G3/B5 were associated with IgG of type 3E4/H8. The use of these four mAb as immunoadsorbents allowed the purification of two IgG and two Ig populations. When assayed in vivo by passive transfer experiments in recipient monkeys previously infected by P. falciparum, protection could be associated with the IgG or Ig populations of type 3F11/G10-3A2/G6. In contrast, recipient animals which received the IgG type 3E4/H8 or Ig type 4G3/B5 presented rapidly evolving parasitemia similar to that in animals which received non-immune IgG or protective immune sera depleted of the above Ig or IgG fractions. The identification of protective and non-protective Ig populations will help in the evaluation of vaccine candidates against P. falciparum.

Animals↗

PubMedDate not supplied

[Isolation and partial study of an anti-hemoglobine precipitine in "Biomphalaria glabrata" (author's transl)].

A protein (PaHb) with a precipiting capacity with regard to normal and pathological human hemoglobin as well as horse and hen hemoglobin has been separated on immunoadsorbent from hemolymph of Biomphalaria glabrata. The joining of PaHb and hemoglobin takes place at the level of the polypeptidic chain. A reconnaissance of the spatial structure of the globin seems to exist. The absence of heme does not lead to a decrease in the intensity of the reaction. The coefficient of the sedimentation of PaHb is of 2.74 S and its molecular weight has been estimated at 47,000 per chromatography in thin layer. The divalent cation MgCl2 strengthens the intensity of the reaction, as for CaCl2 no change is observed, and in the presence of sodium citrate one observes a clear decrease in the reaction. The intensifying of the reaction when in presence of divalent cation MgCl2 could be the result of a stabilization or an activation of the natural structure of PaHb when in presence of Mg. PaHb shows no fonctional impairment after exposure at 65 degrees C during 45 min. The localization of PaHb in the total antigenic structure of the hemolymph is situated around the level of the 5th precipitine line. The functional role of the protein seems to carry the hemoprotein of the hemolymph.

Animals↗

PubMedDate not supplied

Kinetics of the humoral immune response to blood-induced falciparum malaria in the squirrel monkey Saimiri sciureus.

Twenty squirrel monkeys were inoculated with the Palo Alto (FUP) strain of Plasmodium falciparum and treated with quinine one or two weeks after inoculation. Antibody production, measured by the IFA technique, closely followed the appearance of parasites in the blood, rose to a maximum in about two to three weeks, stayed at this level for one to two months and then declined progressively. IgM antibodies appeared faster than any other class of antibody and at two weeks of infection represented 50-80% of total malarial antibodies. IgM antibodies also declined more rapidly and reached barely detectable levels within two to three months. IgG antibodies rose slowly to a maximal level which was, however, maintained for a longer period. No significant differences were observed between intact and splenectomized monkeys. Challenge with virulent parasites two months after the initial infection showed that both groups of monkeys, particularly the intact ones, had acquired a strong protective immunity. The secondary IgG response was stronger when the challenge was performed more than two months after the primo-inoculation.

Animals↗