Here is an interesting concept.
We know that in Hyper IgM syndrome, there is an inability to undergo normal class-switching or somatic hypermutation in B cells.
It is characterized by normal level of B cells with diminished levels of IgG, IgE and IgA and with high levels of IgM.
That is why, these patients are susceptible to infections by extracellular pathogens that require class-switched antibodies for clearance, such as pyogenic bacteria.
But why would it predispose to P jirovecii (P. carni) infections? Pneumocystis doesn't require antibodies for clearance!
We know that in Hyper IgM syndrome, there is an inability to undergo normal class-switching or somatic hypermutation in B cells.
It is characterized by normal level of B cells with diminished levels of IgG, IgE and IgA and with high levels of IgM.
That is why, these patients are susceptible to infections by extracellular pathogens that require class-switched antibodies for clearance, such as pyogenic bacteria.