Difference Between Primary Lymphoid Organs and Secondary Lymphoid Organs

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What are Primary Lymphoid Organs?

Primary lymphoid organs are the centers of the immune system where lymphocyte development and maturation occur. That is to say, they are responsible for the lymphocyte proliferation, differentiation and maturation. The initial cells in primary lymphoid organs are therefore the undifferentiated stem cells in the lymphoids. Such sites provide the environment in which the stem cells grow into either T cells or B cells.

In addition, bone marrow is a type of primary lymphoid organ, where lymphoid stem cells proliferate and differentiate. Therefore, these stem cells are differentiated into both T lymphocytes and B lymphocytes in the bone marrow. Immature T cells then travel through the blood to the thymus, which is another primary lymphoid organ for maturation. But B lymphocyte maturation occurs in the bone marrow itself.

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What are the Secondary Lymphoid Organs?

Secondary lymphoid organs are the locations of the immune system, where lymphocytes are functionally specialized by allowing them to come into contact with different antigens. Such organs therefore form an array of filters in order to collect antigens, which always track the contents of the extracellular fluid including the blood, tissue fluid, and lymph. Some examples of secondary lymphoid organs are lymph nodes, tonsils, spleen, Peyer's patches, mucosa - associated lymphoid tissue (MALT), etc.

In addition, about 100 - 200 lymph nodes are present in the body, encapsulating the lymphoid tissue. We are mostly concentrated in the back, thorax, abdomen, and pelvis. They have lymphocytes T and B, as well as antigen-capture macrophages. MALT is also responsible for filtering the fluid in tissues. The tissue is about 1 mm tiny in diameter. This exists in the digestive tract, oral passage, nasopharyngeal tract, thyroid, breast, lung, salivary glands, hair, and skin. Often, three different MALT cases are tonsils, Peyer's spots, and appendix. Significantly, all of the above secondary lymphoid organs contain T and B lymphocytes as well as antigen-capture macrophages.

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Similarities Between Primary and Secondary Lymphoid Organs

  • Two structures in the body which assist the immune system are primary and secondary lymphoid organs.

  • They provide a stationary structure for producing, maturing and interacting migratory immune cells with antigens

Difference Between Primary and Secondary Lymphoid Organs


Primary lymphoid organs refer to immune system organs in which lymphocytes form and mature while secondary immune organs refer to immune system organs that maintain mature naive lymphocytes and initiate an adaptive immune response. This is the major difference between lymphoid organs of primary and secondary origin.


Their function represents a significant difference between primary and secondary lymphoid organs. Primary lymphoid organs allow lymphoid stem cells to proliferate, differentiate, and mature while secondary lymphoid organs encourage functional lymphoid cells to grow.

Types of Lymphocytes

In addition, primary lymphoid organs contain only T cells or B cells, while secondary lymphoid organs contain T cells and B cells , respectively.

Contact with Antigens

A further difference between primary and secondary lymphoid organs is contact with antigens. Primary lymphoid organs have no antigen contact whilst secondary lymphoid organs have antigen contact.

With Age

Primary lymphoid organs suffer age - related atrophy while secondary lymphoid organs increase size by age. This is another difference between lymphoid primary and secondary

Primary Lymphoid Organs Versus Secondary Lymphoid Organs

Primary Lymphoid Organs

Secondary Lymphoid Organs

Organs of immune system where lymphocytes are made and mature.

Organs of immune system which sustain mature naive lymphocytes and begin an adaptive immune response.

They let lymphoid stem cells to proliferate, differentiate and mature

They let lymphoid cells to become functional

These organs contain either T-cells or B-cells

These organs contain both T-cells and B-cells

They have no contact with antigens

They have contact with antigens

These organs undergo atrophy with age

These organs increase in size with age

FAQ (Frequently Asked Questions)

Q1. What is the difference between Primary and Secondary Lymphoid Organs?

Ans. The other primary lymphoid tissue is the thymus, the location where marrow progenitor cells differentiate into mature cells derived from the thymus (T). Secondary lymphoid tissues are locations where lymphocytes and nonlymphoid cells associate with each other to produce immune responses to antigens.

Q2. What are Secondary Lymphoid Organs?

Ans. Secondary lymphoid organs (SLOs) include lymph nodes (LNs), spleen, Peyer's patches (PPs), and mucosal tissue— NALT, Adenoids, and Tonsils.

Q3. What are Primary and Secondary Organs?

Ans. In humans one distinguishes between primary lymphatic organs and secondary ones. The lymphocytes develop in the main lymph organs to become immunocompetent cells, and emigrate to the secondary lymph organs. There they are responsible for mounting the body 's particular protection.

Q4. What are Primary Lymphoids?

Ans. Lymphocytes are the primary lymphatic organs where they develop and mature. They provide a dividing and maturing environment for stem cells into B-and T-cells: There are two primary lymph organs: the red bone marrow and the thymus gland. The bone marrow' born' in both T - cells and B - cells.