The binding force between antigen and antibody is due to three factors. They are
(i) closeness between antigen and antibody
(ii) non-covalent bonds or intermolecular forces and
(iii) affinity of antibody.

They functions as antibodies. The functions of immunoglobulin are agglutination, precipitation, opsonisation, neutralization etc.,

Antibodies are classified into five major categories based an physiological and biochemical properties. They are IgG (gamma), IgM (rnu), IgA (alpha), IgD (delta) and IgE (epsilon).

Substances that can enhance the immune response to an antigen are called adjuvants.

Haptens are substance that are nonimmunogenic but can react with the products of a specific immune response.

Killer cells are type of T lymphocytes which move around the body and destroy cells which are damaged or infected.

Helper T cells are a type of T lymphocytes and release a chemical called cytokine which activates B lymphocyte.

(i) Bone marrow is a lymphoid tissue found within the spongy portion of the bone.
(ii) Bone marrow contains stem cells known as haematopoietic cells.
(iii) They have the potential to multiply through cell division and either remain as stem cells or differentiate and mature into different kinds of blood cells.

The process of production of blood cells in the bone marrow is called haematopoiesis.

It is the first one to encounter the antigen that enters the tissue spaces. Lymph nodes filter and trap substances that travel through the lymphatic fluid.

MALT stands for Mucosa - Associated Lymphoid Tissue.
BALT stands for Bronchial / Tracheal - Associated Lymphoid Tissue.
These are the examples of secondary lymphoid organs.

The thymus is a flat and bilobed organ located behind the sternum, above the heart.

The immunity that an individual acquires after birth is known as acquired immunity. It is the body's resistance to a specific pathogen.

Innate immunity is the natural phenomenon of resistance to infection which an individual possesses right from the birth.

The overall ability of body to fight against the disease causing pathogen is called Immunity.