Visualizing the T-cell response elicited by oral administration of soluble protein antigen

Oral administration of soluble protein antigen induces tolerance, while particulate antigens encountered in the intestine provoke active immunity. Although the events that lead to these distinct outcomes are not yet fully characterized, they may reflect differences at the antigen-presenting cell (APC) level. The role of dendritic cells (DC) in regulating responses at mucosal sites has remained largely undefined because of the low frequency of DC in mucosal-associated tissues. In this study we have used the growth factor Flt3-ligand (Flt3L) to expand DC populations in vivo, in combination with an adoptive transfer system, in order to track antigen-specific T cells during oral tolerance induction. We observed rapid T-cell activation, localized particularly in the mucosal tissues, within hours after feeding the soluble protein antigen, ovalbumin (OVA). The response was enhanced in Flt3L-treated mice, indicating an important role for DC during the inductive phase of tolerance.

Expanding dendritic cells in vivo enhances the induction of oral tolerance

The intestine is under perpetual challenge from both pathogens and essential nutrients, yet the mucosal immune system is able to discriminate effectively between harmful and innocuous Ags. It is likely that this selective immunoregulation is dependent on the nature of the APC at sites where gut Ags are processed and presented. Dendritic cells (DC) are considered the most potent of APC and are renowned for their immunostimulatory role in the initiation of immune responses. To investigate the role of DC in regulating the homeostatic balance between mucosal immunity and tolerance, we treated mice with Flt3 ligand (Flt3L), a growth factor that expands DC in vivo, and assessed subsequent systemic immune responsiveness using mouse models of oral tolerance. Surprisingly, mice treated with Flt3L to expand DC exhibited more profound systemic tolerance after they were fed soluble Ag. Most notably, tolerance could be induced in Flt3L-treated mice using very low doses of Ag that were ineffective in control animals. These findings contrast with the generally accepted view of DC as immunostimulatory APC and furthermore suggest a pivotal role for DC during the induction of tolerance following mucosal administration of Ag.

Palmar sweating as a function of failure in preschool children

The purpose of this study was to determine the extent to which failure precipitates physiological arousal (palmar sweating) in kindergarten children. High interfinger and interobserver reliability were repotted on measurements of palmar sweating collected from children of varying socioeconomic, residential, and early school backgrounds; however, for none of these children did palmar sweating increase differentially contingent upon failure as contrasted with success. The lack of significant differences between success and failure groups may raise questions regarding the interpretation of studies with young children in which manipulations of failure are expected to affect learning or performance variables.