Regulated exopolysaccharide production in Myxococcus xanthus. (1/592)

Myxococcus xanthus fibrils are cell surface-associated structures composed of roughly equal amounts of polysaccharide and protein. The level of M. xanthus polysaccharide production under different conditions in the wild type and in several mutants known to have alterations in fibril production was investigated. Wild-type exopolysaccharide increased significantly as cells entered the stationary phase of growth or upon addition of Ca2+ to growing cells, and the polysaccharide-induced cells exhibited an enhanced capacity for cell-cell agglutination. The activity of the key gluconeogenic pathway enzyme phosphoenolpyruvate carboxykinase (Pck) also increased under these conditions. Most fibril-deficient mutants failed to produce polysaccharide in a stationary-phase- or Ca2+-dependent fashion. However, regulation of Pck activity was generally unimpaired in these mutant strains. In an stk mutant, which overproduces fibrils, polysaccharide production and Pck activity were constitutively high under the conditions tested. Polysaccharide production increased in most fibril-deficient strains when an stk mutant allele was present, indicating that these fibril-deficient mutants retained the basic cellular components required for fibril polysaccharide production. In contrast to other divalent cations tested, Sr2+ effectively replaced Ca2+ in stimulating polysaccharide production, and either Ca2+ or Sr2+ was required for fruiting-body formation by wild-type cells. By using transmission electron microscopy of freeze-substituted log-phase wild-type cells, fibril material was observed as a cell surface-associated layer of uniform thickness composed of filaments with an ordered structure.  (+info)

Differential expression of nonagglutinating fimbriae and MR/P pili in swarming colonies of Proteus mirabilis. (2/592)

The expression of nonagglutinating fimbriae (NAF) and mannose-resistant/Proteus-like (MR/P) pili in swarming colonies of Proteus mirabilis was investigated. Elongated swarmer cells do not express pili, and the relative number of bacteria expressing NAF during swarming and early consolidation phases was very low (<5%). Relative expression of NAF in a terrace increased to approximately 30% at 48 h. We also determined the expression of NAF and MR/P pili in two phenotypically distinguishable regions of each terrace. The expression of both NAF and MR/P pili was always higher in the region closer (proximal) to the middle of the colony than in the distal region of the terrace. The relative numbers of bacteria expressing NAF or MR/P pili in the proximal region were between 39.1 and 63% and between 5.9 and 7.7%, respectively. In the distal region, expression levels were between 20.8 and 27.3% and between 3.7 and 5. 6%, respectively. A time course experiment testing NAF expression in both the proximal and distal regions of a terrace indicated that NAF expression in the proximal regions was always higher than in the distal regions and increased to a plateau 40 to 50 h after the start of the swarming phase for any given terrace. These results indicate that expression of NAF or MR/P pili in swarming colonies of P. mirabilis is highly organized, spatially and temporally. The significance of this controlled differentiation remains to be uncovered.  (+info)

Surfactant protein D binds to Mycobacterium tuberculosis bacilli and lipoarabinomannan via carbohydrate-lectin interactions resulting in reduced phagocytosis of the bacteria by macrophages. (3/592)

Surfactant protein-D (SP-D) is a collectin produced in the distal lung airspaces that is believed to play an important role in innate pulmonary immunity. Naive immunologic responses to Mycobacterium tuberculosis (M.tb) are especially important in the lung, since entry of this inhaled pathogen into the alveolar macrophage is a pivotal event in disease pathogenesis. Here we investigated SP-D binding to M.tb and the effect of this binding on the adherence of M. tb to human macrophages. These studies demonstrate specific binding of SP-D to M.tb that is saturable, calcium dependent, and carbohydrate inhibitable. In addition to purified SP-D, SP-D in bronchoalveolar lavage fluids from healthy donors and patients with alveolar proteinosis also binds to M.tb. Incubation of M.tb with SP-D results in agglutination of the bacteria. In contrast to its binding to M.tb, SP-D binds minimally to the avirulent Mycobacterium smegmatis. SP-D binds predominantly to lipoarabinomannan from the virulent Erdman strain of M.tb, but not the lipoarabinomannan from M. smegmatis. The binding of SP-D to Erdman lipoarabinomannan is mediated by the terminal mannosyl oligosaccharides of this lipoglycan. Incubation of M.tb with subagglutinating concentrations of SP-D leads to reduced adherence of the bacteria to macrophages (62.7% of control adherence +/- 3.3% SEM, n = 8), whereas incubation of bacteria with surfactant protein A leads to significantly increased adherence to monocyte-derived macrophages. These data provide evidence for specific binding of SP-D to M. tuberculosis and indicate that SP-D and surfactant protein A serve different roles in the innate host response to this pathogen in the lung.  (+info)

Binding of [125I] wheat germ agglutinin to Chinese hamster ovary cells under conditions which affect the mobility of membrane components. (4/592)

The binding of [125I]wheat germ agglutinin ([125I]WGA) of high specific activity to Chinese hamster ovary (CHO) cells has been examined over a millionfold range of WGA concentrations and correlated with the phenomena of agglutination and capping by WGA. Analysis of the binding data by the method of Scatchard gives a complex curve indicative of positive cooperativity amongst high-affinity binding sites. Binding assays performed under conditions which inhibit capping and/or agglutination, such as low temperature or glutaraldehyde fixation, give similarly complex binding curves. Thus, the gross mobility of WGA receptors in the membrane does not appear to be responsible for the cooperative binding of WGA to CHO cells.  (+info)

Natural polyreactive immunoglobulin A antibodies produced in mouse Peyer's patches. (5/592)

To understand the biological function of natural immunoglobulin A (IgA) antibodies in Peyer's patches (PP), we generated IgA monoclonal antibody (mAb) clones from the PP of normal, unimmunized, specific pathogen-free BALB/c mice and examined their reactivities by enzyme-linked immunosorbent assay (ELISA). Many of these antibodies reacted with more than one antigen examined, suggesting that they were polyreactive Abs. Two mAbs agglutinated several different strains of commensal bacteria isolated from mice. To examine the genetic features of these polyreactive mAbs, the VH genes of seven different IgA mAbs were sequenced. The VH genes from the VGAM, J558 and 7183 families were compared with sequence from the mAbs with distinct VDJ rearrangements. One of the mAbs that agglutinated bacteria was encoded by a germline VH gene, but the VH region of the other polyreactive mAbs contained between seven and 11 mutated sites. No indication of antigenic selection was observed in the pattern of these mutated sites. Our results show that polyreactive IgA Abs are present in PP as a part of the normal B-cell repertoire. These polyreactive Abs may establish a natural immune homeostasis, and function as a polyreactive sensor to detect pathogenic invasion and to control immune response in the gut.  (+info)

Development of antibodies against chondroitin sulfate A-adherent Plasmodium falciparum in pregnant women. (6/592)

In areas where Plasmodium falciparum is endemic, pregnant women are at increased risk for malaria, and this risk is greatest during the first pregnancy. The placenta sequesters parasites that are able to cytoadhere to chondroitin sulfate A (CSA), a molecule expressed by the placental syncytiotrophoblast, while parasites from a nonpregnant host do not bind to CSA. Cytoadherence is mediated by the expression of variants of the P. falciparum-erythrocyte membrane protein 1 family. Each member of this molecule family induces antibodies that specifically agglutinate infected erythrocytes and inhibit their cytoadherence ability. We investigated whether the higher susceptibility of primigravidae was related to the lack of immune response towards CSA-binding parasites. In a cross-sectional study, primigravidae delivering with a noninfected placenta were less likely to have antibodies agglutinating CSA-binding parasites than multigravidae (P < 0.01). In contrast, parasites from nonpregnant hosts were as likely to be recognized by the sera from women of various parities. In a longitudinal study, at 6 months of pregnancy, antibodies against CSA-binding parasites were present in 31.8% of primigravidae and in 76.9% of secundigravidae (P = 0.02). The antibodies against CSA-binding parasites inhibited the cytoadherence of a CSA-adherent parasite strain to the human placental trophoblast. Our data support the idea that the higher susceptibility of primiparae is related to a lack of a specific immune response to placental parasites.  (+info)

Concanavalin A receptors on the surface membrane of lymphocytes from patient's with Hodgkin's disease and other malignant lymphomas. (7/592)

Concanavalin A (Con A) induces movement of its receptors on the cell surface membrane. This induction results in a concentration of Con A site complexes on one pole of the cell to form a cap. A marked difference was found in the mobility of Con A receptor between lymphocytes from normal persons and lymphocytes from patients with Hodgkin's disease and other malignant lymphomas. Lymphocytes isolated from tonsils of patients undergoing tonsillectomy and from axillary lymph nodes of breast cancer patients exhibited approximately 30% of cells with caps, which is identical with the cap formation ability of normal lymphocytes. In biopsy material from patients with Hodgkin's disease and other malignant lymphomas, a significant decrease in the ability of the lymphocytes to form caps was observed. This difference in the mobility of Con A sites was even more pronounced in lymphocytes isolated from the peripheral blood. In 123 patients with Hodgkin's disease and other malignant lymphomas, cap formation ranged between 3 and 12%. The ability of cells, from a normal donor or a lymphoma patient, to form caps was independent of the source from which the lymphocytes were isolated, e.g., lymph node, spleen, or blood. Lymphocytes from patients with lymphoma were also agglutinated by Con A to a higher degree than normal lymphocytes. These findings are discussed in relation to the association of the lymphocytes with these malignancies and as a possible aid in their differential diagnosis.  (+info)

Membrane difference in peripheral blood lymphocytes from patients with chronic lymphocytic leukemia and Hodgkin's disease. (8/592)

Lymphocytes were isolated from the peripheral blood of 21 normal persons and 66 patients with chronic lymphocytic leukemia (CLL), CLL in remission, Hodgkin's disease, Hodgkin's disease in remission, various other tumors, or cardiovascular diseases; The lymphocytes were studied for cap formation and agglutinability by concanavalin A, and for cell attachment to the surface of a petri dish. The frequency of cap formation was lowest in lymphocytes from patients with untreated Hodgkin's disease (2.1 plus or minus 0.8%), next lowest in lymphocytes from patients with CLL who were or were not under treatment (7,0 plus or minus 1;3%), and also low in Hodgkin's disease in remission (10.6 plus or minus 1.2%). The frequencies of cap formation by lymphocytes from patients with various other tumors (19.1 plus or minus 2.5%), with CLL in remission (24.0 plus or minus 0.9%), and with nonmalignant diseases (26.0 plus or minus 2.2%) were more similar to the frequency found in lymphocytes from normal persons (29.4 plus or minus 2.8%). Lymphocytes from all the patients, including those in remission, showed a higher degree of agglutinability by concanavalin A than lymphocytes from normal persons. Cell attachment to a petri dish was highest with CLL, next highest with CLL in remission, and low for normal persons and all the other patients. Lymphocytes from normal persons that consisted predominantly of thymus-derived cells gave similar results to isolated normal bone marrow-derived cells. The results indicate that there were different changes in the surface membrane of lymphocytes from patients with CLL, CLL in remission, Hodgkin's disease, and Hodgkin's disease in remission, and that the patients in clinical remission still showed abnormalities in their lymphocytes.  (+info)

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