Immune system and Immune response

Immune system noun - A system (including the thymus and bone marrow and lymphoid tissues) that protects the body from foreign substances and pathogenic organisms by producing the immune response.

Immune response and immune system are semantically related. In some cases you can use "Immune response" instead a noun phrase "Immune system".

Immune response noun - A bodily defense reaction that recognizes an invading substance (an antigen: such as a virus or fungus or bacteria or transplanted organ) and produces antibodies specific against that antigen.

Immune system and immune response are semantically related. You can use "Immune system" instead a noun phrase "Immune response".