Bacterial stimulation and granulocyte inhibition of granulopoietic factor production

TLR2 mediates recognition of live Staphylococcus epidermidis and clearance of bacteremia

Background

Staphylococcus epidermidis (SE) is a nosocomial pathogen that causes catheter-associated bacteremia in the immunocompromised, including those at the extremes of age, motivating study of host clearance mechanisms. SE-derived soluble components engage TLR2; but additional signaling pathways have also been implicated, and TLR2 can play complex, at times detrimental, roles in host defense against other Staphylococcal spp. The role of TLR2 in responses of primary blood leukocytes to live SE and in clearance of SE bacteremia, the most common clinical manifestation of SE infection, is unknown.

Methodology/Principal Findings

We studied TLR2-mediated recognition of live clinical SE strain 1457 employing TLR2-transfected cells, neutralizing anti-TLR antibodies and TLR2-deficient mice. TLR2 mediated SE-induced cytokine production in human embryonic kidney cells, human whole blood and murine primary macrophages, in part via recognition of a soluble TLR2 agonist. After i.v. challenge with SE, early (1 h) cytokine/chemokine production and subsequent clearance of bacteremia (24–48 h) were markedly impaired in TLR2-deficient mice.

Conclusions/Significance

TLR2 mediates recognition of live SE and clearance of SE bacteremia in vivo.

Release of growth promotors from mononuclear human blood cells by LPS, lectins and lithium, as tested in the mouse CFU-C assay

Medium (MCM, 20% human serum), conditioned for 24 h by mononuclear human blood cells, had no colony-forming ability when tested in the mouse CFU-C assay. However, when combined with L-CSF, which predominantly generates macrophage colonies, MCM increased the colony number and size. Even more significant was the increased cellularity with a striking shift towards granulocyte production. Some human sera induced GIF formation without additives, but mostly LPS was required. After heat inactivation, all sera became dependent on LPS to yield an active MCM. Lithium, PHA, Con A and PMW also stimulated GIF formation, which itself depended upon protein synthesis. Heat inactivation of LPS and serum did not reduce their ability, in combination, to yield an active MCM. However, when serum and LPS were mixed before heat treatment, the ability to induce GIF production was abolished, but could be restored by adding intact LPS. This may indicate that LPS exerts its effect by combining with a serum factor yielding a heat-sensitive complex. However, even in the absence of serum, LPS had a stimulatory effect when used in large concentrations, but still the MCM was less active than MCM with serum.

Schistosomal stimulation of eosinophil production by human bone marrow in vitro

These studies were undertaken to determine if schistosomal and ragweed antigens incubated with human peripheral blood mononuclear cells (MNC) would stimulate the production of an eosinophil colony stimulating factor (CSF) which was active on human bone marrow. These studies have shown that schistosoma mansoni antigen in a concentration of 5 micrograms/ml incubated with MNC's from unsensitized individuals lead to production of a conditioned medium which did not stimulate an increased number of total colonies but did increase the number of eosinophil colonies (44 to 61 colonies). Ragweed antigen also stimulated increased eosinophil CSF (from 44 to 63 colonies). The granulocyte response to parasitic antigens almost invariably involves the eosinophil system. Eosinophils play a vital role in the control of these diseases in humans. Further understanding of the interaction of parasitic antigens with the granulopoietic system will hopefully give new and important clues as to how such parasites interact with man and how they are controlled.

Regulation of the colony-stimulating activity produced by a murine marrow-derived cell line (H-1)

The production of molecular species that stimulate growth of granulocyte or macrophage colonies (GM-CSF) by the fibroblastoid H-1 cell line is unaffected by either native or iron-saturated lactoferrin, although some inhibition is detected with 10 microM prostaglandin E1. The H-1 GM-CSF is able to support the formation of macrophage, neutrophil, and mixed colonies. Feeder layers of H-1 cells are also able to support the development of colony-forming units stimulated by GM-CSF (GM-CFUc) although the number of colonies produced when the optimal H-1 cell concentration is plated (2.5 x 10(3) cells) is only 30% of the number with conditioned medium alone. This inhibitory effect is observed irrespective of the presence of an additional agar layer between the feeder cells and plated bone marrow cells, implying that diffusable substances are involved. Addition of indomethacin (10 microM) to feeder layers derived from 2.5 x 10(3) H-1 cells increases the number of GM-CFUc detected to 50% of that seen with conditioned medium alone. This result suggests that released prostaglandin may be responsible for some, but not all, of the observed inhibition of colony formation. In the presence of the H-1 feeder layers, only macrophage colonies are detected and hence it appears that the H-1 cells produce, in addition to prostaglandin, a diffusible inhibitory substance that preferentially inhibits granulopoiesis.

Implications of leukocytosis and fever at conclusion of antibiotic therapy for intra-abdominal sepsis

Outcomes of 65 patients after operation who had exhibited a clinical response to treatment for intra-abdominal sepsis were compared based on the presence or absence of leukocytosis and fever at the conclusion of antibiotic therapy. Fifty-one patients were afebrile when antibiotics were stopped. Intra-abdominal infection developed in 7 of 21 (33%) who had a persistent leukocytosis, but no intra-abdominal infections developed after operation in 30 patients who had normal WBC counts at the end of antibiotic treatment (p less than 0.005). Nosocomial infections developed in 6 (12%) of the 51 patients, and there was no difference in the incidence between patients with or without leukocytosis. Eleven of 14 (79%) patients who were still febrile when antibiotics were discontinued developed infections after operation. Nosocomial infections occurred in three (21%) and intra-abdominal infections in eight (57%). Of the 15 patients who developed intra-abdominal infection after operation, only four responded to appropriate antibiotic treatment without requiring further surgery. The other patients required surgical management for definitive control within two months of the initial operation. In conclusion, patients at risk of developing infection after operation after exhibiting a clinical response to treatment of intra-abdominal sepsis are those who are afebrile with a persistent leukocytosis or who are still febrile when antibiotics are stopped.

Regulation of granulopoiesis and distribution of granulocytes in early phase of bacterial infection

Studies have been carried out to determine the effect of bacterial infection on CSF production, CFU-C activation, and bacterial clearance by mature granulocytes in mice infected with Escherichia coli. These studies have shown that immediately after bacterial infection (5 minutes), serum colony-stimulating factor (CSF) levels and bone marrow colony-forming units in culture (CFU-C) levels are elevated. This is followed by oscillatory rises in both of these parameters and the appearance of granulocytes in the infected site. With clearance of bacteria, CSF and CFU-C levels return to normal. These studies have indicated further that bacterial infection is a major stimulus for granulocyte production through the CSF-CFU-C system and that clearance of bacteria by mature granulocytes may serve as a negative feedback regulatory arm.

Adherent cell dependent colony-stimulating activity in human serum: A granulopoietic regulator?

Bacterial infections and trauma which increase production of granulocytes and monocytes by the bone marrow, may do so through factors in serum capable of stimulating growth of granulocyte-macrophage cells in vitro. Human serum possesses two types of colony stimulating activity (CSA), one which stimulates granulopoietic progenitor cells directly, and another which results from the interaction of serum and bone marrow adherent cells (monocyte-macrophages) or peripheral blood leucocytes: adherent cell dependent CSA. These activities are due to different factors which may be separated by gel filtration. Sera of 7 patients undergoing hystectomy who developed post-operative infection showed post-operative elevation of the adherent cell dependent activity in all cases but no change in direct acting CSA. These results suggest that the direct acting CSA in human serum does not represent the principal humoral 'message' to the bone marrow from sites of trauma and infection in the tissues and that granulopoiesis may be controlled indirectly by the action of a different humoral factor which increases production of CSA by marrow monocyte-macrophages. Preliminary experiments suggest that lymphocytes stimulated by bacterial products be one source of this factor.

Control factors of granulopoiesis in human serum

The role of serum factors in the modulation of production of colony-stimulating activity (CSA) has been investigated. A factor has been described, and partially characterized, in human serum that has the capacity to stimulate increased synthesis and release of CSA by human mononuclear cells (MNC). MNC RNA and protein synthesis are required to demonstrate this effect of serum, but DNA synthesis and mitotic division are not required. The factor in serum resulting in this effect is a heat-labile protein with a molecular weight slightly greater than that of CSA.