A number of preclinical studies over the past decade have shown the beneficial effects of Lactobacillus johnsonii in delaying T1DM onset, which is proposed to be mediated by a number of processes, including suppression of Th17 cells, increasing intestinal crypt Paneth cell numbers, and suppressing gastro-intestinal caspase-1 induction [70,71,72], whilst also decreasing the kynurenine/tryptophan ratio, increasing cytotoxic CD8+ T cells, and changing the patterned immune response, as shown in healthy human volunteers [73]. Here, CD8A is linked to type 1 diabetes mellitus.