Aridity Gradients Shape Intraspecific Variability of Morphological Traits in Native Ceratonia siliqua L. of Morocco.

The carob tree (Ceratonia siliqua L.) is a significant fruit tree in the Mediterranean region with cultural, biological, and ecological importance. Despite its importance, intraspecific trait variability (ITV) in carob trees has been largely overlooked in previous studies. Understanding ITV and its relationship with environmental conditions is crucial for conservation and breeding programs. In this study, we investigated the variability of carob pod and seed-related traits across different ecological scales in 25 studied populations in Morocco. Significant differences in morphological traits were observed between carob populations at various ecological levels, and pod-related traits exhibited greater variability than seed traits. Correlation analysis revealed strong associations between carob morphological traits and environmental conditions, with altitude and aridity index playing an influential role. The aridity gradient was strongly related to changes in pod size, seed number, and size, as well as seed yield. Our findings highlight an important ITV reaching 45% at the intra-population level, 36.5% at the inter-geographic level, and 30% at the inter-population level. Overall, this study contributes valuable insights into the ecology and adaptation of carob trees, emphasizing the importance of considering intraspecific variability when studying this remarkable species. This knowledge is critical for addressing the challenges posed by climate change and human activities on the long-term survival and ecological functioning of carob populations.

Secretory IgA-mediated neutralization of Shigella flexneri prevents intestinal tissue destruction by down-regulating inflammatory circuits.

Shigella, a Gram-negative invasive enteropathogenic bacterium responsible for bacillary dysentery, causes the rupture, invasion, and inflammatory destruction of the human colonic mucosa. We explored the mechanisms of protection mediated by Shigella LPS-specific secretory IgA (SIgA), the major mucosal Ab induced upon natural infection. Bacteria, SIgA, or SIgA-S. flexneri immune complexes were administered into rabbit ligated intestinal loops containing a Peyer's patch. After 8 h, localizations of bacteria, SIgA, and SIgA-S. flexneri immune complexes were examined by immunohistochemistry and confocal microscopy imaging. We found that anti-Shigella LPS SIgA, mainly via immune exclusion, prevented Shigella-induced inflammation responsible for the destruction of the intestinal barrier. Besides this luminal trapping, a small proportion of SIgA-S. flexneri immune complexes were shown to enter the rabbit Peyer's patch and were internalized by dendritic cells of the subepithelial dome region. Local inflammatory status was analyzed by quantitative RT-PCR using newly designed primers for rabbit pro- and anti-inflammatory mediator genes. In Peyer's patches exposed to immune complexes, limited up-regulation of the expression of proinflammatory genes, including TNF-alpha, IL-6, Cox-2, and IFN-gamma, was observed, consistent with preserved morphology. In contrast, in Peyer's patches exposed to Shigella alone, high expression of the same mediators was measured, indicating that neutralizing SIgA dampens the proinflammatory properties of Shigella. These results show that in the form of immune complexes, SIgA guarantees both immune exclusion and neutralization of translocated bacteria, thus preserving the intestinal barrier integrity by preventing bacterial-induced inflammation. These findings add to the multiple facets of the noninflammatory properties of SIgA.

Secretory IgA mediates bacterial translocation to dendritic cells in mouse Peyer's patches with restriction to mucosal compartment.

In addition to fulfilling its function of immune exclusion at mucosal surfaces, secretory IgA (SIgA) Ab exhibits the striking feature to adhere selectively to M cells in the mouse and human intestinal Peyer's patches (PPs). Subsequent uptake drives the SIgA Ab to dendritic cells (DCs), which become partially activated. Using freshly isolated mouse DCs, we found that the interaction with SIgA was tissue and DC subtype dependent. Only DCs isolated from PPs and mesenteric lymph nodes interacted with the Ab. CD11c(+)CD11b(+) DCs internalized SIgA, while CD11c(+)CD19(+) DCs only bound SIgA on their surface, and no interaction occurred with CD11c(+)CD8alpha(+) DCs. We next examined whether SIgA could deliver a sizeable cargo to PP DCs in vivo by administering SIgA-Shigella flexneri immune complexes into a mouse ligated intestinal loop containing a PP. We found that such immune complexes entered the PPs and were internalized by subepithelial dome PP DCs, in contrast to S. flexneri alone that did not penetrate the intestinal epithelium in mice. Dissemination of intraepithelial S. flexneri delivered as immune complexes was limited to PPs and mesenteric lymph nodes. We propose that preexisting SIgA Abs associated with microbes contribute to mucosal defense by eliciting responses that prevent overreaction while maintaining productive immunity.