Until recently the concept of immunomodulation in patients with severe sepsis (formerly called sepsis syndrome or septic shock) appeared very promising. Research has focused on the possible therapeutic potential of interfering with cytokine pathways, either by preventing the induction of cytokines, such as TNF-alpha, by neutralization of lipopolysaccharide (LPS), or through the use of agents that attenuate cytokine action. Nowadays research on protein or protein constructs with antibacterial activities such as bacterial/permeability increasing protein (BPI), platelet activating factor receptor antagonists, nitric oxide and cyclo-oxygenase inhibitors, are still being followed. In large clinical trials monoclonal antibodies against core glycolipid (E5, HAIA) were shown to be at best of only marginal benefit, and in some trials results were indecisive. Also, the results with IL-lra, although initially heralded with high expectation, were at the end disappointing and the trials discontinued. Two large trials with monoclonal antibodies against TNF showed some effect in subcategories of patients: a third trial is on its way. Other phase I; II studies include those of soluble TNF receptors and BPI. The area of immunomodulation has now become an area of more realism and the results of early trials has forced investigators to go back the drawing board and to re-investigate the whole concept of immunotherapy and immunoprophylaxis.

A total of 174 blood isolates of Escherichia coli, collected during a 5-year period at the University Hospital Utrecht, were serotyped with rabbit sera against 171 0 antigens and 73 capsule (K) antigens. The four most prevalent 0-antigen serotypes were 06 (n = 22), 018 (n = 19), 01 (n = 19), and 02 (n = 15). Thirty-one strains were not typeable with any of the 0-antigen-typing sera. Of the 148 strains that were subjected to K-antigen serotyping, 34 strains lacked a K antigen and 41 were not typeable with the K-antigen-specific antisera used in the study. Ki was by far the most frequently found K-antigen serotype; this was followed by K2, K53, K5, K13, K7, K(A)28, and K15. Strains possessing a Kl antigen were further classified as either 0-acetyl-positive (n = 12) or 0-acetyl-negative (n = 21) strains. Retrospective analysis of patients infected with different E. coli isolates-nonencapsulated (n = 23), 0-acetylated Ki (n = 12), and non-0-acetylated Ki (n = 21)-revealed clinical differences. More patients suffered from sepsis (94% versus 74%), and a higher rate of mortality was found in the group infected with Kl isolates (18 versus 9%v) than in the group infected with nonencapsulated isolates. More patients with severe sepsis (25 versus 10%) and a higher mortality (33 versus 10%o) were found in the group infected with 0-acetylated Kl isolates than in the group infected with non-0-acetylated isolates. Also, the hospitalization of these patients was prolonged. Thus, 0-acetylated E. coli Kl strains seem to be more virulent than non-0-acetylated Kl strains.

To study antibody-mediated protection against Escherichia coli peritonitis in BALB/c mice, monoclonal antibodies (MAbs) were generated against the capsule (K5) and the lipopolysaccharide (O18) of E. coli. Flow cytometric analysis with two selected immunoglobulin M MAbs revealed that bacteria were antigenically heterogeneous. Arbitrarily, three subpopulations in E. coli O18K5 cultures could be distinguished by double immunofluorescence. A subpopulation bound only the anti-K5 MAb, and another subpopulation bound only the anti-O18 MAb. An intermediate subpopulation, however, bound both MAbs. In agreement with this result, combinations of both MAbs enhanced phagocytosis of fluorescein isothiocyanate-labeled bacteria by human polymorphonuclear leukocytes and mouse macrophage J774 cells as well. In protection experiments, combinations of both MAbs, preincubated with 3 50% lethal doses of E. coli O18K5, protected all mice upon intraperitoneal challenge. Relatively high doses of either MAb alone proved to be not fully protective in this infection model. Protection of mice by the combination of MAbs was associated with significantly lower (P < 0.02) tumor necrosis factor levels in serum 90 min after challenge compared with any other treatment group. Similarly, prophylactic administration of MAbs yielded significantly lower (P < 0.01) tumor necrosis factor levels in mice that received the combination of MAbs than in any other treatment group.

Flow cytometry revealed that the binding of immunoglobulin M monoclonal antibodies (MAbs) to Escherichia coli O18K5 was modulated by exposure of the bacteria to subinhibitory concentrations of imipenem. The binding of anti-K5 MAb was decreased, while the binding of anti-O18 MAb was increased. In addition, anti-lipid A MAbs bound only to imipenem-treated bacteria. The biological effect of MAb binding was investigated in BALB/c mice by determination of the levels of bacteremia, tumor necrosis factor (TNF) in serum and survival after intraperitoneal challenge with bacteria preincubated with MAb. Neither MAb alone (150 micrograms per animal) proved to be protective against untreated bacteria. Anti-lipid A MAb on its own, in contrast to anti-K5 and anti-O18 MAbs, was not protective against imipenem-treated bacteria. Only combinations which included anti-O18 MAb and anti-K5 MAb exerted in mice enhanced protection against smooth E. coli O18K5 as well as imipenem-treated E. coli O18K5. This was reflected by reduced TNF levels in serum and increased survival. The addition of anti-lipid A MAb to the combination of anti-K5 MAb and anti-O18 MAb reduced serum TNF levels in mice, but not significantly.

Here we have used hybrid mouse IgG1-2a and IgG2a-2b mAb to demonstrate that the interaction between the human high-affinity IgG FcR (huFc gamma RI) and monomeric mouse IgG2a mAb requires only one of the mIgG2a H chains. Recently, we reported a method for the generation and isolation of hybrid hybridomas, producing hybrid mouse mAb. Using this method we have obtained hybrid mouse (m)IgG1-2a and mIgG2a-2b mAb reacting with either horseradish peroxidase or human IgA1 (monospecific mAb) or with both Ag (bispecific mAb). Using protein A- or Ag-affinity chromatography purified hybrid mAb, we demonstrate here the binding of monomeric hybrid mIgG1-2a and mIgG2a-2b mAb to huFc gamma R on U937 cells, whereas no binding could be observed to the K562 cell line. Monomeric mouse IgG2a mAb and human IgG1 were found to be capable of inhibiting the binding of these hybrid mIgG1-2a and mIgG2a-2b mAb in a manner similar to the way they inhibited binding of monomeric mIgG2a mAb to U937 cells; this is in contrast to our findings for mIgG1 and mIgG2b mAb which did not inhibit the binding of both hybrid mAb. In addition, the binding of the hybrid mIgG1-2a and mIgG2a-2b mAb could be blocked by mAb TB-3, which is known to block huFc gamma RI-mediated binding by the "Kurlander phenomenon" and not by the anti-Fc gamma RII mAb CIKM5 and IV.3. These results indicate that both types of monomeric hybrid mAb are bound by the huFc gamma RI. Scatchard plots of mIgG2a, hybrid mIgG1-2a, and mIgG2a-2b mAb binding revealed similar numbers of binding sites and similar affinity constants of huFc gamma RI for these mAb (0.9 to 3.6 x 10(8) M-1). These results suggest that huFc gamma RI, present on the U937 cell line, are capable of binding monomeric hybrid mIgG1-2a and mIgG2a-2b mAb, and that this interaction requires only one of the mIgG2a H chains.