Mycobacterium avium subspecies paratuberculosis (MAP) has been previously associated to T1D as a putative environmental agent triggering or accelerating the disease in Sardinian and Italian populations. Our aim was to investigate the role of MAP in T1D development by evaluating levels of antibodies directed against MAP epitopes and their human homologs corresponding to ZnT8 and proinsulin (PI) in 54 T1D at-risk children from mainland Italy and 42 healthy controls (HCs). A higher prevalence was detected for MAP/ZnT8 pairs (62,96% T1D vs. 7,14% HCs; p < 0.0001) compared to MAP/PI epitopes (22,22% T1D vs. 9,52% HCs) and decreasing trends were observed upon time-point analyses for most peptides. Similarly, classical ZnT8 Abs and GADA decreased in a time-dependent manner, whereas IAA titers increased by 12%. Responses in 0–9 year-old children were stronger than in 10–18 age group (75% vs. 69,1%; p < 0.04). Younger age, female sex and concomitant autoimmune disorders contributed to a stronger seroreactivity suggesting a possible implication of MAP in multiple autoimmune syndrome. Cross-reactivity of the homologous epitopes was reflected by a high correlation coefficient (r2 > 0.8) and a pairwise overlap of positivity (>83% for MAP/ZnT8).

The missense PTPN22 C1858T polymorphism recently emerged as an important population-independent risk factor for type 1 diabetes (T1D) and other autoimmune diseases. The PTPN22 gene encodes the lymphoid tyrosine phosphatase (LYP), a negative regulator of signal transduction through the T-cell receptor. Although the frequency of the polymorphism is variable among different ethnic groups, the association between PTPN22 *T1858 and T1D has been replicated in several populations. Here, we contribute the first replication of the association between PTPN22 and T1D in populations from continental Italy, carried out in two independent samples of T1D patients (N = 216 and 82) and controls (N = 271 and 89). Our data also suggest that T1D carriers of the *T1858 allele could be at increased risk for other comorbid autoimmune disorders.

There are several pieces of evidence indicating that Mycobacterium avium subspecies paratuberculosis (MAP) infection is linked to type 1 diabetes (T1D) in Sardinian patients. An association between MAP and T1D was recently observed in an Italian cohort of pediatric T1D individuals, characterized by a different genetic background. It is interesting to confirm the prevalence of anti-MAP antibodies (Abs) in another pediatric population from continental Italy, looking at several markers of MAP presence. New-onset T1D children, compared to age-matched healthy controls (HCs), were tested by indirect enzyme-linked immunosorbent assay for the presence of Abs toward the immunodominant MAP3865c/ZnT8 homologues epitopes, the recently identified C-terminal MAP3865c281-287 epitope and MAP-specific protein MptD. Abs against MAP and ZnT8 epitopes were more prevalent in the sera of new-onset T1D children compared to HCs. These findings support the view that MAP3865c/ZnT8 cross-reactivity is involved in the pathogenesis of T1D, and addition of Abs against these peptides to the panel of existing T1D biomarkers should be considered. It is important now to investigate the timing of MAP infection during prospective follow-up in at-risk children to elucidate whether Ab-titers against these MAP/ZnT8 epitopes are present before T1D onset and if so if they wane after diagnosis.