 It has been hypothesized that the condition represents a state of heightened sensitivity to antigenic stimuli , with cross @-@ reactivity of the resulting cell @-@ mediated immune response with cells of the epithelium . Some hypothesize that aphthous stomatitis is caused by expression of HLA class II antigens along with the normally found HLA class I antigens in epithelial cells , which results in them being recognized by the immune system as foreign cells rather than self . Various antigenic triggers have been implicated as a trigger , including L forms of streptococci , herpes simplex virus , varicella @-@ zoster virus , adenovirus , and cytomegalovirus . 
