MPO and amyotrophic lateral sclerosis: For CFA/I antigen, the subjects who did not seroconvert had higher concentrations of pre-challenge MPO than the subjects who did seroconvert both in serum (IgA 5.2 fold higher, p = .0014; IgG 2.5 fold higher) and in ALS (IgA 2.4 fold higher, p = .0831), (Figure a-c, Table 2).