Answer:
This question is incomplete because of the absence of options
Step-by-step explanation:
Serum ELISA test is based on antigen-antibody interaction (which is the immune mechanism referred to in the question). Both antigen and antibodies are proteins and thus can be referred to as large molecules. In some cases, the ELISA test kit wells are coated with antibodies that are specific to choice antigens in the serum while in some other cases the wells are coated with antigens that are specific to choice antibodies in the serum. Thus, either antibody or antigen (both proteins) present in the serum can evoke an immune response (depending on what the well is coated with) which causes a reaction to proceed; this reaction can be determined by a microplate reader.
From the above, it can be deduced that either the antigens or the antibodies can evoke an immune response.