Studies of short-term pulmonary and peripheral vascular responses induced in oophorectomized sheep by the infusion of a group B streptococcal extract

Group B Streptococcus, phospholipids and pulmonary hypertension

OBJECTIVE

Group B Streptococcus is the most common cause of bacterial infection in the newborn. Our aim was to purify and identify molecules produced by the bacterium, which cause pulmonary hypertension.

STUDY DESIGN

Guided by bioassays performed in neonatal lambs, we utilized standard biochemical techniques for the purification of these bioactive compounds. The compounds were identified by mass spectrometry. Fully synthetic compounds were then tested using the bioassay to confirm their ability to induce pulmonary hypertension.

RESULT

The purified bacterial components causing pulmonary hypertension were the phospholipids cardiolipin and phosphatidylglycerol. Synthetic cardiolipin or phosphatidylglycerol also induced pulmonary hypertension in lambs.

CONCLUSION

Bacterial phospholipids are capable of causing pulmonary hypertension. This finding opens new avenues for therapeutic intervention in persistent pulmonary hypertension of the newborn and generates hypotheses regarding the etiology of respiratory distress in the newborn and the possible effect of antibiotic therapy.

Group B streptococcal phospholipid causes pulmonary hypertension

Group B Streptococcus is the most common cause of bacterial infection in the newborn. Infection in many cases causes persistent pulmonary hypertension, which impairs gas exchange in the lung. We purified the bacterial components causing pulmonary hypertension and identified them as cardiolipin and phosphatidylglycerol. Synthetic cardiolipin or phosphatidylglycerol also induced pulmonary hypertension in lambs. The recognition that bacterial phospholipids may cause pulmonary hypertension in newborns with Group B streptococcal infection opens new avenues for therapeutic intervention.

The fatty acid composition of maternal diet affects lung prostaglandin E2 levels and survival from group B streptococcal sepsis in neonatal rat pups

Dietary fatty acid effects upon the immune system may be mediated in part by effects upon the synthesis of proinflammatory mediators. The effects of maternal dietary fatty acid composition upon lung prostaglandin (PG) E2 levels and survival from group B streptococcal (GBS) infection were investigated in neonatal rat pups. Beginning on d 2 of gestation and throughout lactation, pregnant dams were fed a purified diet whose fat source (22% of energy) was either corn oil or menhaden fish oil. On postnatal d 3, pups were randomly cross-fostered to dams of the same diet group to minimize litter effects; litters were then culled to 10 pups per dam. On postnatal d 7, pups were either injected with 1 x 10(7.5) GBS organisms or were killed for determination of lung tissue levels of PGE2 and lung and erythrocyte fatty acid composition. Arachidonic acid and PGE2 levels were significantly higher in the lungs of pups in the corn oil group compared with the fish oil group. Forty-nine percent of pups in the corn oil group survived the GBS challenge compared with 79% of pups in the fish oil group (P = 0.0005). These data suggest that the fatty acid composition of pre- and/or postnatal diet affects the neonatal response to immune challenge, which may be due in part to effects upon the synthesis of pro-inflammatory mediators.

Group B Streptococcus and E. coli LPS-induced NO-dependent hyporesponsiveness to noradrenaline in isolated intrapulmonary arteries of neonatal piglets

1. The effects of endotoxin (E. coli lipopolysaccharide, LPS) and heat inactivated group B Streptococcus (GBS) were studied on the contractile responses to noradrenaline (NA) in isolated pulmonary arteries and on the activity of the constitutive and inducible nitric oxide synthase (NOS) in lung fragments of neonatal piglets. 2. Short-term (< or = 5 h) incubation with LPS (1 micrograms ml-1) or GBS (3 x 10(7) colonies forming units ml-1) did not modify the vascular responsiveness to NA (10(-8) M-10(-4) M) in isolated intrapulmonary arteries. However, long-term incubation (20 h) with LPS or GBS produced a significant reduction in the maximal contractile responses and shifted the concentration-response curve for NA downwards. 3. Endothelium removal or the cyclo-oxygenase inhibitor meclofenamate (10(-5) M) did not affect the GBS- and LPS-induced hyporesponsiveness to NA. 4. The presence of the nitric oxide (NO) precursor, L-arginine (10(-5) M), 30 min prior to the contractility challenge increased the LPS- and GBS-induced pulmonary vascular hyporesponsiveness to NA. In contrast, the addition, prior to the challenge with NA, of the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 10(-4) M) or coincubation with dexamethasone (3 x 10(-6) M), a potent inhibitor of the induction of NOS, or with the protein synthesis inhibitor cycloheximide (10(-5) M) completely restored the reactivity to NA in LPS- and GBS-treated pulmonary arteries. 5. The incubation for 20 h of lung fragments with LPS and GBS produced a significant increase in the Ca2+-independent (inducible) NOS activity determined by the conversion of radiolabelled L-arginine to citrulline, but did not modify the constitutive NOS activity. This NOS induction was abolished by coincubation with dexamethasone (3 X 10-6 M).6. These results demonstrated that prolonged incubation with GBS and LPS causes an induction of NOS activity which results in a reduced vascular responsiveness to NA in pulmonary arteries of neonatal piglets. Thus, induction of NOS seems to be responsible for the delayed pulmonary vascular hyporesponsiveness induced by GBS (a Gram-positive) and E. coli (a Gram-negative), the most common causal agents of neonatal sepsis.

Induction of tumor necrosis factor alpha by the group- and type-specific polysaccharides from type III group B streptococci

Previous studies suggested that circulating tumor necrosis factor alpha (TNF-alpha) may have a pathophysiologic role in experimental neonatal sepsis induced by group B streptococci (GBS). This study was undertaken to investigate the ability of the type III and group-specific polysaccharides of GBS to induce TNF-alpha production and TNF-alpha-dependent lethality in neonatal rats. The cytokine was detected in plasma samples by the L929 cytotoxicity assay. Intracardiac injections of either polysaccharide induced dose-dependent, transient elevations in plasma TNF-alpha levels that returned to baseline values after 5 h. The group-specific antigen induced significantly higher mean peak TNF-alpha levels than the type III antigen (125 +/- 47 versus 44 +/- 15 U/ml with 70 mg/kg of body weight). Glycogen (70 mg/kg), used as a negative control, did not induce TNF-alpha. The lipopolysaccharide-neutralizing agent polymyxin B did not decrease TNF-alpha levels induced by either polysaccharide, ruling out contamination with endotoxin as a possible cause of TNF-alpha induction. Fifty percent lethal doses of the type III and group-specific antigens given as intracardiac injections were 105 and 16 mg/kg, respectively. Salmonella endotoxin, used as a positive control, had a 50% lethal dose of 0.1 mg/kg. The lethal activities of GBS polysaccharides, as well as endotoxin, were completely prevented by pretreatment of neonatal rats with the respective specific antibodies or anti-murine TNF-alpha serum. To assess the relative importance of the type-specific substance in TNF-alpha induction by whole bacteria, two unrelated GBS transposon mutants devoid of only the type-specific capsular polysaccharide (COH1-13 and COH31-15) were employed. Each of the heat-killed unencapsulated mutants was able to produce plasma TNF-alpha level elevations or TNF-alpha-dependent lethality but was significantly less efficient in these activities than the corresponding encapsulated wild-type strain. These data suggest that the presence of type-specific material on GBS is not necessary for the stimulation of TNF-alpha production. Type III capsular polysaccharide, however, can significantly increase the ability of GBS to induce TNF-alpha. Further studies will be needed to assess the importance of TNF-alpha induction by the group- and type-specific antigens in the pathophysiology of GBS disease.

Production of tumor necrosis factor by human cells in vitro and in vivo, induced by group B streptococci

Tumor necrosis factor alpha (TNF alpha) has been implicated as one of the major mediators of the gram-negative septic shock syndrome. In our studies, group B streptococci (GBS) induced the production of TNF alpha by human mononuclear cells in a dose- and time-dependent manner. Human mixed mononuclear cell cultures exposed to an encapsulated (657.6 +/- 71.3 pg/ml; n = 30 preparations) or an unencapsulated transposon mutant of type III GBS (755.8 +/- 54.7 pg/ml; n = 9) produced similar amounts of TNF alpha. Isolated monocytes and culture-derived macrophages produced higher amounts of TNF alpha (1565 +/- 211 and 1790 +/- 928 pg/ml respectively) in response to GBS than did mixed mononuclear cell cultures. In response to GBS, mixed mononuclear cells from neonates produced significantly more TNF alpha (729.1 +/- 45 vs 520.3 +/- 47.2 pg/ml; p = 0.004) than did cells from adults. Examination of specimens from patients with neonatal GBS disease revealed detectable levels of TNF alpha (7 to 424 pg/ml) in the serum of 5 of 10 patients with sepsis, in 5 of 5 urine samples from infants with sepsis, and in the cerebrospinal fluid of 1 patient with meningitis. These results suggest both a major role for TNF alpha in the pathogenesis of human neonatal GBS sepsis and shock and a potential role for immunotherapy directed against this cytokine in this fulminant neonatal bacterial infection.

Outbreak of respiratory syncytial virus in France

A report is given of an outbreak of respiratory syncytial virus infection in a neonatal unit in France. Twenty-three of 32 infants were infected (72%) despite infection control procedures. Prophylactic administration of non-specific gamma globulins was associated with a significant decrease in infection rate (p less than 0.05). The administration of transfer factor to infected infants was also associated with a significantly lower rate of severe respiratory diseases (p less than 0.05).