Following a blood infection, the first class of antibodies produced by the immune system are IgM antibodies. They form the “vanguard” of the immune response, before other cells are activated to fight the infection. Some people are deficient or completely lack these antibodies, so that they develop congenital immune deficiency. Researchers have now discovered how this deficiency can also lead to an increased risk of arteriosclerosis and consequently even to serious cardiovascular diseases.