Perturbing gut microbiota early in life can lead to the development of autoimmunity. We are just beginning to unravel how early immune programming by microbiota may have long-term effects on noncommunicable diseases. In this thesis, we lay groundwork for programming of the immune system by commensal bacteria early in life through our studies on the induction of early endogenous neonatal IgA, and we evaluate Limosilactobacillus reuteri's characteristics as an inducer. Garnering attention for use a probiotic, L. reuteri has many proven health promoting benefits, such as IgA induction, but emerging evidence also links specific strains to autoimmune disease. "Super-induction" of neonatal IgA can be achieved through cross-fostering immunocompetent pups on immunocompromised dams. We found that this phenomenon was categorically due to transferal of microbes from dam to offspring. By comparing strain CF48-3A to the non-gastric-related organism L. oris, we discovered that L. reuteri is a microorganism that can enhance early neonatal IgA induction. Further investigations revealed that the ability to induce neonatal IgA is not ubiquitous in all L. reuteri strains, as ATCC PTA 6475 did not significantly elevate IgA. We discovered that 6475 has the antigenic ability to stimulate B cell differentiation and IgA production, but it is suppressed by a mechanism related to differences in surface architecture of this strain. L. reuteri strains also vary in their potency of aryl hydrocarbon receptor (AhR) stimulation. In mice, activation of AhR during gestation by a potent prototypical ligand, TCDD, leads to development of autoimmunity offspring. We found that TCDD exacerbated autoimmunity in adult mice using a strain of mice with similar AhR affinity to humans. Further investigations can clarify whether differential AhR ligand expression between L. reuteri strains contributes to the relationship between L. reuteri and autoimmunity. Overall, we conclude that differences between strains of L. reuteri have profoundly different immunological consequences that contribute to our understanding of the linkage between strains and autoimmunity. / Doctor of Philosophy / Differences in microbes transferred to infants through maternal routes shapes the early development of the immune system. In general, transferred microbes are healthy for the infant, and studies suggest that disruption of healthy microbes in the infant gut is linked to long-term health consequences, like autoimmune diseases. We found that a particular difference in maternally transferred microbes increases the early appearance of immunoglobulin A (IgA, a gut-related antibody) in neonatal mice, which is an antibody important for protecting against gut-related infections. We were able to link this early IgA production to a probiotic species Limosilactobacillus reuteri. Within the species classification as L. reuteri, several genetically different strains are health-promoting and broadly marketed over-the-counter for use in probiotic supplements for infants, children, and pregnant and nursing mothers. Emerging scientific evidence also points to a potential connection between other L. reuteri strains and autoimmune disease. Secreted products of genetically different L. reuteri strains have been discovered to activate aryl hydrocarbon receptor (AhR) with various potency. We used a prototypical AhR ligand and found exacerbation of autoimmune disease in adult mice. Thus, we have concluded that different strains of L. reuteri have broadly different effects on immune system development, and strain variability may explain the different effects on autoimmunity that have been observed.

Mjölksyrabakterier är mikroorganismer som bildar mjölksyra när de bryter ned socker. Dessa bakterier förekommer naturligt i människans kropp och tillhör tarmens normalflora. De hjälper dessutom till med att skydda människan från patogena mikroorganismer. Maten som intas idag innehåller mycket lite av mjölksyrabakterier och bör därför berikas på annat sätt. BioGaia som är ett svenskt bioteknikföretag, har forskat på mjölksyrabakterien Limosilactobacillus reuteri och substansen reuterin. BioGaias produkter innehåller mjölksyrabakterien Limosilactobacillus reuteri som bidrar till en balanserad tarmflora. Stabilitetsstudier är en viktig aspekt när en ny produkt utvecklas där produktens hållbarhet behöver undersökas under olika förhållanden. Haltbestämningen som är en del av stabilitetsstudien, görs idag på bakterier i de olika produkterna på BioGaia med plattmetoden, d.v.s. bakterieodlingar. Processen för plattmetoden tar cirka tre dagar tills att ett resultat kan fås. Syftet med studien var att jämföra plattmetoden med flödescytometri på probiotiska prover, för att se om resultatet av haltbestämningen av antalet levande bakterier blir samma med de olika metoderna och om det är möjligt att ersätta plattmetoden med flödescytometri för probiotiska prover. Studien har visat att skillnaden mellan resultatet från plattmetoden och flödescytometrin på probiotiska prover, är större än förväntat. Storleken på skillnaden varierar mellan prover. Resultatet har dock inte ett tydligt mönster som gör det möjligt att avgöra ifall det är möjligt att ersätta plattmetoden med flödescytometri.