Research Interests

The overall goal of our past and present research activities is to understand cellular and molecular mechanisms governing the interaction between the gastrointestinal tract and the immune response. Interactions between the immune response and the gastrointestinal tract may occur at several levels, three of which have become the focus of our investigations:

• Development of the gut-associated immune system (GALT) in omnivorous birds: influences of gastro-intestinal development, bacterial colonization and nutrition.

• Immune related function s of the intestinal epithelial cell (IEC)

• Development of tolerance or response following intestinal (oral or rectal) intake of antigen.

Effects of gastro-intestinal development on mucosal immune competence

Many omnivorous birds begin foraging immediately after hatch. This means that they become immediately exposed to adult-type food and environmental bacteria at a time where the intestinal tract is still tuned to an embryonic environment. Hence, to survive, the digestive tract of these birds must undergo rapid development in terms of digestive and protective capacities. The goals of our research are directed towards describing the mechanism by which GALT undergoes this rapid development, and how it protects the hatchling from succumbing at an early age to environmental pathogens. To investigate the development of the avian GALT we have developed numerous tools that allow investigation of GALT development at the level of the gene, protein and cell.

Several of our major findings are:

• Adaptive immunity in the avian GALT becomes fully functional (only) during the second week of life.

• Innate immune systems and maternal antibodies protect chicks during the first week of life.

• Impaired gut development leads to delayed maturation of GALT.

• Bacterial colonization has significant impact on development of GALT in the hindgut.

Immune-related functions of the avian IEC

The IEC has a central role in digestion and absorption functions in the gut. In the mammal, it is now widely accepted that the IEC functions as an immune sentinel with signaling properties. These properties include cognitive interactions with neighboring immune cells (i.e. dendritic cells, NKT cells and many more), and may include transfer of IEC stress during pathogen attack. The avian IEC has to date been shown include very few immune response properties. This deficiency in knowledge is due mainly to difficulties in culturing avian IEC in vitro. We have, for some time now, made attempts to culture IEC with little success; recently, however, we have managed to decipher some of the requirements of these cells, and are now proceeding to a more detailed analysis of immune-related functions of the avian IEC.

Several of our major observations are:

• Avian IEC are extremely fragile in culture, but with the correct conditions may be cultured for at least 36 hours and for as long as 15 days.

• Toll like receptors are constitutively expressed by these cells, and they can be selectively induced to up- or down-regulate these receptors.

• Avian IEC respond very well to bacterial LPS.

• Avian IEC express the poly-Ig-receptor for IgA

Tolerance or response following intestinal exposure to antigen

Oral vaccines provide a major means to vaccinate large populations at a low cost. This approach is of particular interest to the poultry industry in which major vaccination programs include the inoculation of individual chicks in flocks containing over 100,000 birds. One of the main issues in development of intestinal vaccines is to be able to predict the immunogenicity and consequential protection of the designed vaccine. The immunological properties of the vaccine depend on the structure of the vaccine itself and on the interaction between the immunogen and the intestinal immune system. A given protein antigen can be either immunogenic or tolerogenic depending on the circumstances it is encountered by the immune system. Thus, protein antigens administered orally can frequently induce immune tolerance (oral tolerance), while if administered by parenteral injection – they will induce robust immun responses. Hence, with the aim of developing potent oral-vaccination strategies, we are interested in investigating mechanisms responsible for oral tolerance, and in developing strategies for oral immunization - and particularly so in poultry. Again, the entire research program focused on the quest to develop efficient oral vaccines for poultry.

Several of our major findings are:

• We were the first to publish that clonal anergy is a mechanism for oral tolerance.

• Oral tolerance can be demonstrated for both Th1 and Th2 phenotypes.

• The co-stimulatory molecule CTLA-4 is involved in generation of peripheral tolerance.

• Birds are surprisingly different from mammals in that oral antigen usually leads to response rather than tolerance.

• Oral tolerance may be induced in very young chicks with immature intestinal systems.