Impaired phagocytosis and opsonisation towards group B streptococci in preterm neonates

Abstract

Aims-To study the chemiluminescence response in polymorphonuclear leucocytes (PMNL) at diVerent stages of maturity and the opsonic capacity of sera with defined titres of anti-capsular type III antibodies, after exposure to serotype III group B streptococci (GBS). The influence of GBS type III capsule expression on PMNL chemiluminescence response was also investigated. Methods-Two clinical isolates of serotype III GBS and two serotype III reference strains which form isogenic variants with high and low amounts of capsule substance, respectively, were used. PMNL and sera were obtained from adult healthy blood donors, full term neonates, and preterm neonates. Results-PMNL from premature infants showed a significantly lower chemiluminescence response (p<0.0001) than the PMNL from adults and neonates, while the chemiluminescence response with adult, neonatal, and preterm sera gradually diminished. In the presence of a serum pool with a standardised complement value, raised (>10 mg/l), rather than low (<1.0 mg/l) anti-III antibody titres induced a higher chemiluminescence response to the capsule expressing variant. When GBS were cultured at pH 5.0, the bacteria had a higher buoyant density, reflecting decreased expression of capsule substance compared with bacteria grown at pH 7.4. Concomitantly, there was a substantial increase in chemiluminescence response for all isolates cultured at the lower pH, except for the capsule deficient mutant. Conclusions-PMNL function and opsonic capacity are significantly impaired in neonates and correlate with maturation of the newborn child. The combined defect in cellular and humoral defences in preterm neonates may contribute to their increased susceptibility to GBS infection. Growth conditions for GBS, simulating diVerent in vivo environments, greatly aVect capsule expression and resistance to phagocytosis.

Expression of Fc-Gamma Receptors of Neutrophils in Preterm Infants of Different Gestational Age

“…Результаты ограниченного числа исследо-ваний свидетельствуют о том, что большая часть состав-ляющих указанной выше системы неактивна у детей с ОНМТ и ЭНМТ в той же степени, что и у доношенных новорожденных, детей младшего и старшего возраста и взрослых [5][6][7].…”

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6,0 (5,3;9,8),7,1 (5,1;11,5) и 4,27 (2,4;5,8) MFI соответственно (p = 0,013). Экспрессия CD16 у недоношенных, напротив, была ниже: 99,7 (71,3; 126,0) и 80,9 (58,7; 114,8) и 125,3 (95,5; 144,1) MFI соответственно (p = 0,021)

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“…Экспрессия CD16 у недоношенных, напротив, была ниже: 99,7 (71,3; 126,0) и 80,9 (58,7; 114,8) и 125,3 (95,5; 144,1) MFI соответственно (p = 0,021). К концу 1-го мес жизни у недоношенных новорожденных экспрессия CD16 нейтрофилами периферической крови уве-личилась до 126,6 (110,1; 129,0) MFI у детей с ОНТ и до 118,5 (99,5; 132,2 20 preterm infants with LBW, 9.8), 7.1 (5.1; 11.5), and 4.27 (2.4; 5.8) MFI respectively (p = 0.013).…”

Does IVIg administration yield improved immune function in very premature neonates?

“…32 Furthermore, opsonization has little effect in the absence of competent cellular function that is required to engulf and kill the pathogens after effective opsonization. Preterm (28-34 weeks GA) neonates exhibit decreased PMN opsonic capacity, phagocytosis and respiratory burst compared with term neonates and adults, 15 and this may be worse in very premature neonates. 33,34 Improvements in cellular function (phagocytic function and H 2 O 2 production) following IVIg administration were shown in a cohort of nine preterm neonates (average GA, 33 weeks).…”

“…Available evidence indicates that much of this complex system does not function in very premature neonates in the same manner as in more mature neonates, children or adults. [14][15][16][17][18] In neonates, administration of IVIg may improve immune responses by binding to cell surface receptors, provision of opsonophagocytic activity, including activation of complement, promotion of antibody-dependent cytotoxicity and improvement of neutrophil (PMN, polymorphonuclear leukocyte) respiratory burst. 7,19 Additional effects of IVIg may include a reduction of an overexuberant inflammatory reaction that may accompany severe sepsis or septic shock.…”