Which immunoglobulin class is indicative of neonatal infection in infants at birth?

The immunoglobulin class that is indicative of neonatal infection in infants at birth is IgM. This is because IgM is the first antibody produced in response to an infection and is typically detectable in the serum when the immune system encounters a pathogen for the first time. In the case of newborns, the presence of IgM suggests that the infant has been exposed to an infection in utero or during the birthing process, which can be a sign of a congenital infection or an early exposure to pathogens.

IgM does not cross the placenta effectively, so its detection in a newborn's blood indicates that it was produced by the infant's own immune system rather than acquired from the mother. Consequently, the presence of IgM antibodies is a strong indicator of a neonatal infection.

Other immunoglobulins, such as IgG and IgA, play different roles in immunity. While IgG can cross the placenta and provide passive immunity to the fetus, it does not specifically indicate infection because it can be present due to maternal transfer. IgA is more relevant in mucosal immunity and is not typically measured as an indicator of systemic infection in neonates. IgE is primarily associated with allergic responses and parasitic infections, and is also not used as a marker