- Number of responder mice is shown per myelin peptide, with between brackets the mean ratio of antigen-specific spot count over background spot count ± standard deviation. The following responder criteria were used: per 106 splenocytes, the mean antigen-specific spot count must be greater than or equal to 15 spots per well and at least 1.5 times as high as the background reactivity (i.e., the spot count in the negative control). pi post induction