Human interleukin-28B (IL-28B), molecular model. Interleukins a group of secreted proteins and signalling molecules that play a range of roles in cellular communication, particularly within the immune system. IL-28 plays a role in immune defence against viruses. It comes in two forms, A and B. The B-form is also known as interferon lambda 3 (IFNL3). It is thought that the IL-28 interleukins form part of the IL-10 family of interleukins. The structure consists of four protein chains (red, green, yellow, blue).