B cells


B cells are a type of white blood cell that play a central role in the body’s immune system. Their primary role is to help protect you from infections by recognizing harmful substances, such as bacteria, viruses, and toxins, and responding to them. In humans, they develop and mature in the bone marrow.

What do B cells do?

B cells are best known for making antibodies, which are special proteins that attach to germs or other harmful invaders. Antibodies act like “tags,” marking the invader so other immune cells know to destroy it.

In addition to producing antibodies, B cells also:

  • Help the immune system remember past infections, allowing the body to respond more quickly if the same infection comes back.

  • Work with other immune cells, such as T cells, to strengthen and guide the overall immune response.

This ability to both fight infection and provide long-term memory is why vaccines work: they stimulate B cells to make antibodies and remember the infection without causing illness.

Where are B cells found in the body?

B cells are widely distributed throughout the immune system. They are found in lymph nodes, the spleen, tonsils, and the bone marrow.

They also circulate in the bloodstream and can move into tissues where infection is taking place. These locations give B cells the best chance to encounter and respond to harmful invaders.

What types of cancer start from B cells?

When B cells grow out of control, they can form cancers called B-cell lymphomas or leukemias. Common examples include:

These cancers may appear in lymph nodes, bone marrow, spleen, or other tissues. The type of B-cell cancer and where it develops will guide treatment decisions.

What do B cells look like under the microscope?

Under the microscope, B cells usually appear as small, round cells with a dark nucleus and a thin rim of lighter-staining cytoplasm around it. Because B cells can look very similar to other immune cells, pathologists often use special tests such as immunohistochemistry or flow cytometry to identify proteins that are unique to B cells. These tests help confirm that the cells are B cells and can also provide information about whether they are normal or cancerous.

B cell

Why are B cells important in pathology reports?

B cells are often mentioned in pathology reports when tissue samples are examined for signs of infection, inflammation, or cancer. Identifying whether B cells are present, how many there are, and whether they are normal or abnormal provides important clues for diagnosis. For example, finding abnormal B cells may help diagnose a lymphoma, while seeing increased numbers of normal B cells may be a sign of an immune response to infection.

Questions to ask your doctor

  • Why were B cells mentioned in my pathology report?

  • Are the B cells normal, or do they show signs of disease?

  • Could these findings suggest lymphoma, leukemia, or another immune condition?

  • Were special tests performed to identify the B cells?

  • How do these findings affect my treatment or follow-up plan?

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