Willemien C. van Dijk

Escherichia coli antibodies in opsonisation and protection against infection.

The opsonic and protective capacities of rabbit antisera against Escherichia coli O, K and core-glycolipid cell-wall antigens were compared with specific antibody titres as measured by agglutination and enzyme-linked immunosorbent assay. Anti-O antisera were opsonic and protective against two noncapsulate strains. Only anti-K antisera were opsonic and protective against a K-antigen-containing strain. In a mouse model anti-core-glycolipid antiserum was not protective against challenge even by a strain bearing only core glycolipid.

Contact activation by bacterial fragments

Introduction The generation of bradykinin, a vasoactive peptide, capable of decreasing the blood pressure and increasing capillary permeability, has been implicated in the pathogenesis of bacterial shock. We demonstrated recently that the plasma level of all factors of the contact activation system, involved in the liberation of bradykinin, namely Hageman Factor (Factor XII), prekallikrein and high molecular weight kininogen had normal levels in patients with uncomplicated bacteremia, but were significantly decreased during the development of bacterial shock [1]. Although the observed decrease may be due to consumption of these factors, little is known about the initiating mechanism, participating in the pathophysiologie process. Therefore, we investigated the interaction between isolated cell wall components of gram positive and gram negative bacteria and the purified components of the contact activation of human plasma. We present evidence that contact activation can be elicited by bacterial fragments.

The effect of influenza virus on human polymorphonuclear leukocytes

Many viral infections predispose to bacterial superinfections (Martin et al., 1959). Staphylococcal and pneumococcal pneumonia are serious complications during influenza virus infection. It has been suggested that the increased susceptibility for bacteria during virus infection is due to the effect of the viruses on the immune system and on the phagocytic cells (Stuart-Harris, 1979; Larson and Blades, 1976). However, the mechanisms by which the viruses affect neutrophil functions are not well understood. Therefore, we studied the function of polymorphonuclear leukocytes (PMNs) after incubation with influenza virus. PMNs were purified from venous blood drawn from healthy donors as was previously described (Verbrugh et al., 1978). Influenza strain type A Texas 77 (H3N2) was used in all experiments. The phagocytosis ofstaphylococcibyPMNs was studied using [3H]thymidine-labeled bacteria. The uptake of radioactivity by PMNs was used as measure for phagocytosis (Verhoef et al., 1977). The oxidative metabolism of the PMNs was studied by measuring chemiluminescence produced by the PMNs in a liquid scintillation spectrometer (Mills et al., 1978). Chemotaxis of the PMNs was measured under agarose as was described by Nelson, Quie and Summons (1975). Virus-treated PMNs phagoeytized significantly fewer bacteria then did control PMNs. After incubation with 500 HAI units of influenza virus PMNs ingested only 35 ~ of the bacteria, whereas o~ntrol leukocytes ingested over 80 ~ of the added staphylococci. Influenza virus also affected the mobility of the PMNs; while control PMNs migrated 1.2 mm under agarose during 24 h of incubation towards zymosan-activated serum as an attractant, virus-treated cells migrated only 0.5 mm. Influenza virus also had a markedly suppressive effect on chemiluminescence. In each of four experiments neutrophils produced less than 5 ~ of the chemiluminescence produced by the controls. Summarizing, influenza virus specifically inhibited phagocyto sis, oxidative metabolism and chemotaxis by PMNs. We are currently studying the basis of this effect, induced by influenza virus.

Gram-negative Rod Bacteraemia: function of phagocytic cells and opsonic activity of serum

Serious infections due to gram-negative micro-organisms have been increasing over the last decade. Despite aggressive antimicrobial therapy the mortality of these infections is still high. Data on pathogenesis of these infections are conflicting. Therefore, the phagocytic and bactericidal functions of polymorphonuclear leucocytes (PMNs) and monocytes (MNs) and the opsonic activity of serum from patients with gram-negative bacillaemia were evaluated. Leucocytes from five of 20 patients (25 ~) showed diminished phagocytic cell function; in three of the patients the chemotactic activity of leucocytes was also decreased. Compared with normal serum, none of 37 patient sera tested had defects in levels of immunoglobulins, CH s o and C 3. Forty-nine percent of 75 patients were infected with bacterial strains that were poorly opsonized in normal serum. Thirty percent of the isolates were also ineffectively opsonized in the corresponding patients serum. In some patients an increase in opsonic activity due to heat-stable opsonins was found after two weeks. Impaired opsonization of E. coli strains correlated with the presence of K-capsular polysaccharide in bacteria. It was concluded that impaired leucocyte function and ineffective opsonization play a role in the pathogenesis of gram-negative bacteraemia. Specific heat stable opsonins (presumably specific antibodies), appear to be necessary for effective phagocytosis of gram-negative blood isolates.

Sensitivity to serum and phagocytosis by polymorphonuclear leucocytes ofE. coli

Serious infections due to gram-negative microorganisms are increasing over the last decades. Despite aggressive antimicrobial therapy the mortality of these infections is still high. Data on the pathogenesis of these infections are conflicting. Opsonic antibodies against the 0 specific side chains oflipopolysaccharide in the cellwall of E. coli, antibodies against core glycolipid, or anti K antigen antibodies, all have been associated with protection of the host to gram-negative rod bateremia (Howard and Glyn, 1971 ; Young et al., 1977). In this study E. coli strains were isolated from stooland bloodcultures. The presence of K antigen in these strains, the sensitivity to serum and the phagocytosis by polymorphonuclear leucocytes of these strains were determined. The bactericidal assay described by Friedliinder (1975) was used to study the sensitivity to serum. 3H-thymidine-labeled E. coli strains were incubated in 20 % human serum for 1 h and after centrifugation at 1600 g the amount of radio-activity in the sediment and supernatant was determined. When no lysis occurred no radio-activity was found in the supernantant. Phagocytosis was studied according to a method previously described (Verhoef et al., 1977, Verbrugh et al., 1978). K antigen was isolated according to Glynn and Howard, 1970. Two out of 12 stool isolates and two out of 14 bacteremia isolates were serum-sensitive (showing more than 50 % lysis of the bacteria). Six of the stool isolates (50 %) were readily pbagocytized by PMNs compared with four of the blood isolates (29 %). Sixteen strains contained K antigen (4 stool isolates and 12 from bloodcultures). All strains containing K antigen were serum-resistant. 88 % of the strains with K antigen were not taken up by PMNs. Phagocytosis is an important host-resistance factor against E. coli infections. K antigen is an important virulence factor of E. co6 strains determining its invasiveness.