Anthrax and Humoral Immunity: What if?
Because anthrax so effectively disables dedritic cellsc (9, 18), much of what is known about the body’s humoral response is based on vaccines. Antibodies have been developed in guinea pigs against the protective antigen (PA), a protein that binds to both lethal factor (LF) and edema factor (EF), allowing it to infiltrate cells. Anti-PA antibody confers protective immunity against B. anthracis. Antibodies have also been developed against LF in guinea pig models that confer immunity, though this immunity is not as effective as live spore vaccines (19). At first glance, this might suggest that, in the event a host were to survive anthrax infection long enough, the adaptive immune system would eventually generate a humoral response.
B. anthracis also Disables B-cells
B. anthracis’s favorite weapon, lethal toxin (LeTx), is also effective against B-cells. While it does not kill them, it is able to enter the cytoplasm and disable the MAPK kinases. This reduces the ability of B-cells to clonally expand in response to IL-4, anti-IgM, or andit-CD40 stimulation. Also, B-cells, stimulated both in vivo and in vitro are not able to produce IgM in response to TLR-2 and TLR-4 ligands (20).
As with any part of the immune system response and anthrax, the conversation is generally focused around B. anthracis’s deft evasion rather than an effective response. There is no literature documenting an effective humoral response against B. anthracis outside cases in which the host has been artificially vaccinated. The lack of a humoral response is due to an effective strategy that disables both B-cells and dendritic cells.