The present invention provides peptide mimics for HLA class II antigens. The peptide mimics were identified by panning phage display peptide libraries with anti-HLA class II monoclonal antibodies. The peptide mimics inhibit the binding of an anti-HLA class II antigen antibody to HLA class II antigen positive cells and also elicit antibodies which can bind to HLA class II antigen positive cells. The identified peptide mimics can be used as immunogens for therapy of diseases related to cells expressing the HLA class II antigen, such as Non-Hodgkins Lymphoma.