Non-infectious environmental antigens as a trigger for the initiation of an autoimmune skin disease

Pemphigus represents a group of organ specific autoimmune blistering disorders of the skin mediated by pathogenic autoantibodies with well-defined antigenic targets. While most of these diseases are sporadic, endemic forms of disease do exist. The endemic form of pemphigus foliaceus (also known as fogo selvagem, FS) exhibits epidemiological features that suggest exposure to hematophagous insect bites are a possible precipitating factor of this autoimmune disease, and provides a unique opportunity to study how environmental factors contribute to autoimmune disease development. FS patients and healthy individuals from endemic regions show an autoreactive IgM response that starts in early childhood and becomes restricted to IgG4 autoantibodies in FS patients. In searching for triggering environmental antigens, we have found that IgG4 and IgE autoantibodies from FS patients cross-react with a salivary antigen from sand flies. The presence of these cross-reactive antibodies and antibody genetic analysis confirming that these antibodies evolve from the same naïve B cells provides compelling evidence that this non-infectious environmental antigen could be the initial target of the autoantibody response in FS. Consequently, FS serves as an ideal model to study the impact of environmental antigens in the development of autoimmune disease.

From the Deep Sea to Everywhere: Environmental Antigens for iNKT Cells

Invariant natural killer T (iNKT) cells are a unique subset of innate T cells that share features with innate NK cells and adaptive memory T cells. The first iNKT cell antigen described was found 1993 in a marine sponge and it took over 10 years for other, bacterial antigens to be described. Given the paucity of known bacterial iNKT cell antigens, it appeared as if iNKT cells play a very specialist role in the protection against few, rare and unusual pathogenic bacteria. However, in the last few years several publications painted a very different picture, suggesting that antigens for iNKT cells are found almost ubiquitous in the environment. These environmental iNKT cell antigens can shape the distribution, phenotype and function of iNKT cells. Here, these recent findings will be reviewed and their implications for the field will be outlined.

New insight into the origin of IgG-bearing cells in the bursa of Fabricius

The bursa of Fabricius is a primary lymphoid organ for B-cell development and gut-associated lymphoid tissue. After hatching, IgG-containing cells with reticular branches are found in the medulla of bursal follicles on frozen sections stained with anti-Cγ antibody, and IgM(+)IgG(+) B cells are detected in single-cell suspension of the bursa. IgG-containing cells in the medulla do not biosynthesize IgG and are composed of aggregated maternal IgG and environmental antigens. Then, those cells in the medulla are acknowledged as follicular dendritic cells retaining immune complexes. Also, it is presumed that IgM(+)IgG(+) B cells are generated by the attachment of immune complexes to IgM(+) bursal B cells because IgM(+)IgG(+) B cells are induced by antigen-dependent attachment of maternal IgG. Therefore, it is reasonable to suppose that immune complexes exert further B-cell differentiation in the medulla.