Non-Hodgkin lymphoma

The term non-Hodgkin lymphoma, sometimes called NHL, can be broken down. Lymph- refers to lymphocytes and oma- refers to a tumor.

“Non-Hodgkin” refers to the absence of a key cell that’s seen in Hodgkin lymphoma, the Reed-Sternberg cell.

So, non-Hodgkin lymphoma is a tumor derived from lymphocytes - specifically B-cells and T-cells, which mainly live in the lymph nodes and move through the blood and lymphatic system.

Now, B-cell development begins in the bone marrow, which is a primary lymphoid organ. That’s where young precursor B-cells mature into naive B-cells.

The naive B cells then leave the bone marrow and circulate in the blood and eventually settle down in lymph nodes.

Humans have hundreds of lymph nodes, scattered throughout the body, and they’re considered secondary lymphoid organs.

Each lymph node has B-cells which group together in follicles in the cortex or outer part of the lymph node, along with T-cells in the paracortex just below the cortex.

B-cells differentiate into plasma cells, which are found in the medulla or center of the lymph node.

Plasma cells release antibodies or immunoglobulins.

Antibodies bind to pathogens like viruses and bacteria, to help destroy or remove them.

Various immune cells, including B-cells have surface proteins or markers that are called CD, short for cluster of differentiation, along with a number - like CD19 or CD21.

In fact, the combination of surface proteins that are on an immune cell works a bit like an ID card.

Now, a B cell is activated when it encounters an antigen that binds just perfectly to its surface immunoglobulin.

Some of these activated B-cells mature directly into plasma cells and produce IgM antibodies.

Other activated B-cells go to the center of a primary follicle in the lymph node and they differentiate into B-cells called centroblasts and start to proliferate or divide.

These proliferating centroblasts form a germinal center, located in the center of the follicle of the lymph node.

These centroblasts have a rearrangement of their immunoglobulin genes, and some of them undergo a class switch where they change from producing IgM antibodies to producing IgG or IgA antibodies.