Do innate-like B cell responses contribute to neonatal immunity?

The body protects itself from infection via its immune system. We do not completely understand how the immune system works in newborns (either those born at term or prematurely) but we do know that infections are common in this vulnerable patient group and that they can often result in severe illness and death. A better understanding of how this system functions from birth may inform future clinical practice by developing methods to boost the immune response and thereby protect babies. We have already established that T cells, one type of white blood cell that helps protect the body from infection, behave very differently in neonates. We have now identified that a second type of white blood cell, the B cell, that helps protect the body by making antibodies, also exist in different forms in human infants.
In this proposal, we want to scrutinise the biology of this B cell population that is enhanced in neonates and determine its role in protecting babies from infection. We have already collected blood from preterm babies (with their parent's permission and at a time when blood was being taken for routine care) and have samples from babies who were well and from babies during periods of infection. This unique resource will allow us to study the peripheral immune system in neonatal health and disease and look at how these B cells respond in preterm infants. We can compare this to babies born at term by looking in cord blood samples. We will also investigate what these B cells develop into, what type of antibodies they make, and when their predominance starts to decline. We will do this by looking in blood samples taken from babies at 1 and 3 months of age. This may potentially provide a therapeutic target to enhance the neonatal immune system and ultimately reduce morbidity and mortality from infection.

Our main objectives and the methods that will be utilised to achieve them are as follows:
1. Does the innate-like DN B cell respond to infection in neonates? Single cell RNA sequencing analysis of the DN population in cord blood will determine the transcriptional profile of DN cells in healthy term infants and their heterogeneity. We will then assess the transcriptional profile of these cells isolated from preterm infants prior to and during infection. This will determine if these cells are activated in infection and the differentially expressed genes that may drive these responses. BCR analysis will determine if there are any clonal expansions. Activation of DN B cells will be performed in vitro to assess modes of both activation and inhibition to identify how the function of these cells is controlled.
2. What is the progeny of DN B cells? Using an in vitro polarisation protocol (previously published) we will drive the development of antibody secreting cells (ASC) from DN or naïve B cells isolated from the same cord blood samples (on which we have transcriptomic data from Aim 1). We will compare the gene transcription profile between cells generated from these distinct B cell progenitors and also identify any functional differences of the ASC generated via ELISAs to detect both different antibody classes, short- or long-lived ASCs as well as cytokine production.
3: When does DN2 B cell predominance decline? Using flow cytometric analysis on longitudinal samples of infant blood (both those born preterm and at term), we will follow the rise and fall of distinct B cell populations in the human infant and identify whether these trajectories are affected by clinical parameters. Functionality of these cells will be assessed at different times after birth in the term cohort where sample volumes are greater.