What is the role of humoral immunity in the pathophysiology of neonatal sepsis?

Updated: Jun 13, 2019
  • Author: Nathan S Gollehon, MD, FAAP; Chief Editor: Muhammad Aslam, MD  more...
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Answer

The fetus has some preformed immunoglobulin (Ig), which is primarily acquired through nonspecific placental transfer from the mother. Most of this transfer occurs in late gestation, such that lower levels are found with increasing prematurity. The neonate’s ability to generate immunoglobulin in response to antigenic stimulation is intact; however, the magnitude of the response is initially decreased, rapidly rising with increasing postnatal age. [14]

The neonate is also capable of synthesizing IgM in utero at 10 weeks’ gestation; however, IgM levels are generally low at birth, unless the infant was exposed to an infectious agent during the pregnancy, which would have stimulated increased IgM production. [15]

IgG and IgE also may be synthesized in utero. Most IgG is acquired from the mother during late gestation. The neonate may receive IgA from breastfeeding but does not secrete IgA until 2-5 weeks after birth. Response to bacterial polysaccharide antigen is diminished and remains so during the first 2 years of life.

Complement protein production can be detected as early as 6 weeks’ gestation; however, the concentration of the various components of the complement system varies widely from one neonate to another. Although some infants have had complement levels comparable to those in adults, deficiencies appear to be greater in the alternative pathway than in the classic pathway. [16]

The terminal cytotoxic components of the complement cascade that lead to the killing of organisms, especially gram-negative bacteria, are deficient. This deficiency is more marked in preterm infants. Mature complement activity is not attained until infants reach 6-10 months of life. Neonatal sera have reduced opsonic efficiency against GBS, E coli, and Streptococcus pneumoniae because of decreased levels of fibronectin, a serum protein that assists with neutrophil adherence and has opsonic properties.


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