Antigenic heterogeneity of lipopolysaccharide among Burkholderia pseudomallei clinical isolates.

Burkholderia pseudomallei (BP) causes melioidosis, a potentially fatal human infection in the tropics. Clinical isolates from different geographical locations have similar morphological and biochemical characteristics. Although BP has been reported to possess 2 types of lipopolysaccharide (LPS) differing in the chemical structure of their O-polysaccharide (O-PS) component, earlier report demonstrated that the clinical strains exhibited identical LPS moieties. Recently, we reported antigenic similarity between the pathogenic (Ara-) and nonpathogenic (Ara+) biotypes. However, a few clinical isolates showed atypical SDS-PAGE profiles. In this study, LPS from 739 BP isolated from patients and animals in different geographical areas were extracted by proteinase K digestion method. Their SDS-PAGE profiles and their immunoreactivities with patients' sera and monoclonal antibody (MAb) to LPS were analyzed. The isolates showed 3 LPS patterns differing in the number and electrical mobility of bands in silver-stained gel. A majority of BP (711) isolates exhibited identical typical ladder pattern, 21 isolates showed atypical ladder pattern and 7 isolates did not exhibit ladder appearance. However, all LPS preparations exhibited similar endotoxic activity as determined by Limulus amebocyte lysate assay. On the other hand, there were no immunological cross reactivity between typical and atypical LPS, as judged from Western blot against homologous and heterologous sera from melioidosis patients from whom the typical and atypical LPS were isolated. Nevertheless, a Western blot profile of the typical LPS showed some variations when probed with MAb against BP LPS (9D5). Heat-killed bacteria from all LPS groups could similarly activate mouse macrophage cell line to produce nitric oxide (NO) and inducible NO synthase (iNOS).

Thrombocytopenia in malaria.

The relationship between platelet counts and platelet bound (direct) or platelet directed (indirect) serum antibody concentrations was studied in 17 patients with Plasmodium falciparum malaria and 12 patients with P. vivax malaria. Platelet counts rose with recovery from infection from 196 +/- 84 x 10(9)/l (mean +/- SD) and 195 +/- 34 x 10(9)/l to 319 +/- 99 and 283 +/- 62 x 10(9)/l respectively (p less than 0.002), but there was no relationship between either absolute platelet count or changes in counts and either indirect or direct platelet antibody levels. These findings suggest that a non-immunologically mediated mechanism is involved in the pathogenesis of thrombocytopenia in malaria.

Characterization of a monoclonal antibody that neutralizes the hyaluronidase activity of Russell's viper venom.

Three monoclonal antibodies (WPN1, WPN2 and WPN3) raised against a partially purified fraction of Russell's viper venom (RVV) were characterized. All three monoclonal antibodies reacted with crude RVV when tested by ELISA, but only two (WPN1, WPN2) neutralized its hyaluronidase activity. WPN1 was the more potent and was effective at an antigen: antibody ratio of 1:3. Furthermore, WPN1 was shown to recognize only the 14,000 MW component of crude RVV. This has been identified in a previous study to be hyaluronidase. This antibody was also found to recognize some components of Calloselasma rhodostoma venom which also possesses potent hyaluronidase activity. The potential therapeutic role of antibodies that neutralize the hyaluronidase component of snake venoms should be investigated further.

Management of severe malarial infection.

Severe malaria is a major cause of infant and childhood death in the tropics. Effective management relies on rapid diagnosis, prompt administration of parenteral schizonticidal antimalarial drugs, careful fluid balance, prevention of convulsions and early recognition of complications such as hypoglycemia, metabolic acidosis, anemia, pulmonary edema, renal failure, bleeding and supervening bacterial sepsis. The mortality of treated cerebral malaria remains 20%. New, more rapidly acting antimalarials and earlier referral of children with complicated infections should reduce this unacceptable death rate.