083 - Immunity and susceptibility to disease in early infancy

Similar to the last poat (082), this one is about how newborns are surprisingly immune to certain diseases, because they receive disease-targeting antibodies from their mothers. Charles McKhann and Israel Kapnick wrote this review, and sadly there's no new data, but it's a good summary of the topic (for the time).¹

So most interesting is that newborns are immune to several important diseases—measles, scarlet fever, polio, and diphtheria—for up to half a year after birth. This is especially true if their mothers had immunity to those diseases. The duration is impressive because when physicians attempted to produce immunity in people by injecting them with serum from recovered patients (so-called passive immunity, because it is not derived from the patient's own immune system), it only lasted a few weeks at most. Somehow the infant is able to maintain the passive immunity from the mother.

This is not the case with every disease though. Stuff that causes fevers or gut infections and diarrhea, and whooping cough, are not prevented in these newborns quite so well. Other things are intermediate, like chickenpox and pneumonia.

The duration of the immunity might seem to suggest that the antibodies are coming repeatedly from the mother, perhaps from breastmilk, but McKhann and Kapnick say that seems only to happen in cattle, not humans. The evidence seemed to show that infants' passive immunity came through the placenta in the womb. Though it's possible that some components of immunity come through breastmilk and others don't. But it seems possible that antibodies from the placenta get stored up somewhere in the infant.

So the importance of this study as pertains to vaccines is two-fold: first, as discussed in the last post, it may be possible to make the infant immune for some time by vaccinating the mother. Apparently this is pretty helpful with tetanus, as it prevents neonatal tetanus which is common in places in Africa.

Second, it is important for determining when the first vaccines should be given. With stuff like measles, which is an attenuated live virus, if there are already antibodies present, the vaccine won't produce as much of a good response. McKhann and Kapnick recognized this with certain things. So knowing when infants will become susceptible is important for immunizing them at the right time, not too early or too late. For some things, this may be late in the first year of life.

However, immunology is pretty complicated, with things we didn't understand until recently, and things we still don't understand. So it's not clear (to me, anyway) how much of this review is accurate. A later publication made these comments about older reviews, including this one:

"A large and useful part of the data bearing on the immunology of the newborn infant has come from clinical studies of immunizing schedules. There have been many careful reviews of this subject [like this one]...[But] quantitative interpretation of these studies and separation of the factors involved has often been difficult for reasons such as the following: 1. Antigen-antibody reactions may have been used for which there were no accurate methods of titration. Only rough, qualitative conclusions could be drawn. 2. Some studies used antigen-antibody reactions that require complement. The blood of the newborn infant has a low level of complement. This may have caused an undetermined error in the antibody estimation."²

I expect to have more to say in later posts.

References:
1. McKhann, C. F. & Kapnick, I. Immunity and susceptibility to disease in early infancy. The Journal of Pediatrics 13, 907–918 (1938).
2. Osborn, J. J., Dancis, J. & Julia, J. F. Studies of the Immunology of the Newborn Infant 1. Age and Antibody Production. Pediatrics 9, 736–744 (1952).