Explain briefly whether the following statements are true or false : (i) Dendritic cells arise only from the lymphoid organ. (ii) All TH cells express CD4 and recognize only antigen associated with class II MHC molecule. (iii) A hapten can stimulate antibody formation but cannot combine with many different antibody molecules. (iv) In order for B cells to mature into plasma cells, they need help from T cells. (v) All antigens are immunogens but all immunogens are not antigens.

Here is a brief explanation of whether each statement is true or false:

(i) Dendritic cells arise only from the lymphoid organ.

• False: Dendritic cells arise from both lymphoid and non-lymphoid tissues. They originate from hematopoietic stem cells in the bone marrow and migrate to various tissues, including lymphoid organs (like lymph nodes) and peripheral tissues (such as the skin and mucosal surfaces).

(ii) All TH cells express CD4 and recognize only antigen associated with class II MHC molecule.

• True: T helper (TH) cells express the CD4 glycoprotein and recognize antigens that are presented by Class II MHC molecules. This specificity is crucial for their role in helping other immune cells, such as B cells and cytotoxic T cells.

(iii) A hapten can stimulate antibody formation but cannot combine with many different antibody molecules.

• False: A hapten is a small molecule that alone cannot stimulate an immune response or generate antibodies. However, when attached to a larger carrier molecule, it can stimulate an immune response and the antibodies generated can specifically bind to the hapten. The ability of the hapten to combine with different antibodies depends on its ability to bind to the carrier and how it is presented.

(iv) In order for B cells to mature into plasma cells, they need help from T cells.

• True: For most antigens, especially protein antigens, B cells require help from T helper cells to fully mature into plasma cells. This help typically involves the T helper cells providing cytokines and direct contact through surface molecules to support B cell activation and differentiation.

(v) All antigens are immunogens but all immunogens are not antigens.

• False: All immunogens are indeed antigens, but not all antigens are immunogens. An immunogen is a substance that can induce an immune response, while an antigen is a substance that is specifically recognized by the immune system. Some antigens may not be strong enough to elicit an immune response on their own but can still be recognized by immune cells if they are part of a larger immunogenic complex.