The Th1-Th2 classification of cellular immune responses: concepts, current thinking and applications in haematological malignancy

The finding that T cell immune responses could be divided into those promoting cell mediated immunity (Th1) and humoral responses (Th2) has had a profound effect on the understanding of immune response generation over the last 15 years. With ever increasing knowledge of the immune system, the model has come under criticism, as not all responses easily fit the classification. Nonetheless, the model still provides a valuable framework on which to base immunological research. In this review we update the model with current thinking regarding the generation and maintenance of immune responses. We then examine how the Th1–Th2 paradigm may be applied in developing new understanding of several topical issues in haematological malignancy—control of graft-versus–host disease; cytokine control of proliferating clones in B and T cell diseases; and suppression of T cell responses in multiple myeloma.