**Question:** Cells that are identified by the presence of immunoglobulins on the surface include -

A. B lymphocytes
B. T lymphocytes
C. Neutrophils
D. Monocytes

**Core Concept:** Immunoglobulins are a type of antibody produced by the immune system in response to foreign substances, such as bacteria, viruses, or toxins. They are primarily involved in neutralizing pathogens, binding to antigens, and activating the complement system to eliminate these foreign substances. Antibodies are typically present on the surface of specific immune cells, which can be identified by their role in immune response.

**Why the Correct Answer is Right:** Immunoglobulins are proteins produced by B lymphocytes (B cells) in response to antigens. These immunoglobulins bind to antigens and neutralize pathogens, while also activating the complement system to eliminate the foreign substances. Because B cells are responsible for producing these antibodies, they are the cells identified by the presence of immunoglobulins on their surface.

**Why Each Wrong Option is Incorrect:**

A. B lymphocytes are the correct answer, as mentioned above. Antibodies produced by B cells bind to antigens and trigger the immune response. Therefore, B lymphocytes are not identified by the presence of immunoglobulins on their surface.

B. T lymphocytes (T cells) are responsible for regulating the immune response, not producing antibodies. They play a crucial role in activating and coordinating other immune cells, but not in producing immunoglobulins.

C. Neutrophils are granulocytes, a type of white blood cell involved in phagocytosis (engulfing and destroying pathogens) but they do not produce antibodies. Antibodies are produced by B cells and not found on the surface of neutrophils.

D. Monocytes are phagocytic cells involved in the immune response, but they also do not produce antibodies. Antibodies are produced by B cells, not monocytes.

**Clinical Pearl:** Understanding the role of different immune cells in the immune response is crucial for interpreting clinical findings and diagnosing immune system disorders. For example, in cases of agammaglobulinemia, a patient would lack immunoglobulins, making them susceptible to severe infections. In contrast, in cases of hypergammaglobulinemia, there would be excessive immunoglobulins, leading to dysregulated immune response and potential autoimmune diseases.