Mesothelial cells are specialized cells that form a protective lining within the body’s internal cavities and around organs. They can change in response to various stimuli, leading to a state known as “reactivity.” Understanding reactive mesothelial cells is important because their appearance can sometimes mimic more serious conditions, requiring careful evaluation.
Normal Mesothelial Cells
Mesothelial cells form the mesothelium, a thin tissue layer lining the chest, abdominal, and heart cavities, and covering organs like the lungs, intestines, and heart. These cells are typically flat or cube-shaped and have microvilli on their surface. They play several important roles in maintaining bodily function.
They produce lubricating serous fluid, allowing organs to glide smoothly and reducing friction during movements like breathing or digestion. Mesothelial cells also regulate fluid balance by absorbing excess fluid. Furthermore, they contribute to the body’s immune response and tissue repair processes, forming a protective barrier against infections and physical damage.
Causes of Mesothelial Cell Reactivity
Mesothelial cells become reactive when they encounter stress, irritation, or damage within the body cavities they line. This reactivity is a non-specific response, meaning many different factors can trigger it. Inflammation is a common stimulus, often resulting from infections like pneumonia in the lungs or peritonitis in the abdomen.
Physical injury or irritation can also cause mesothelial cells to become reactive, including trauma, surgical procedures, or the presence of foreign bodies. Conditions that lead to fluid buildup in body cavities, such as pleural effusions around the lungs or ascites in the abdomen, can similarly irritate these cells. Underlying benign medical conditions, including liver disease (like cirrhosis), certain kidney disorders (uremia), collagen disorders (such as lupus), or even tissue infarction (like a pulmonary embolism), are also known to induce significant reactive changes in mesothelial cells.
How Reactive Mesothelial Cells Are Identified
Medical professionals identify reactive mesothelial cells primarily through microscopic examination of fluid samples or tissue biopsies. When fluid accumulates in a body cavity, such as pleural fluid from the lungs or peritoneal fluid from the abdomen, it is collected and analyzed. Pathologists then observe these cells under a microscope to detect characteristic changes.
Reactive mesothelial cells often appear enlarged, sometimes up to 50 micrometers in diameter, and can have an altered shape, often described as polyhedral. Their nuclei may be larger than normal with prominent nucleoli. Increased cellular activity can also lead to more frequent cell division (mitotic activity) and the presence of cells with two or more nuclei (binucleation or multinucleation). These cells might form cohesive clusters, sometimes with a scalloped appearance, or display a “two-tone” cytoplasm, where the central part is denser and the periphery is paler.
Interpreting Reactive Mesothelial Cell Findings
The presence of reactive mesothelial cells primarily indicates irritation or inflammation in the body cavity. These cells are not cancerous; they are a benign response to an underlying issue. However, differentiating reactive mesothelial cells from malignant cells can be challenging for pathologists, as they may share similar microscopic features, such as enlarged nuclei or increased mitotic activity.
Due to this potential for overlap, a finding of reactive mesothelial cells alone does not confirm a cancer diagnosis. Further investigation is often needed to determine the precise cause of the cellular changes. Pathologists use various techniques, including immunohistochemical staining, applying specific markers to distinguish between benign and malignant conditions. For instance, reactive mesothelial cells typically stain positive for desmin and negative for epithelial membrane antigen (EMA), whereas malignant mesothelioma cells often show the opposite pattern. The most reliable criterion for identifying a malignant mesothelial proliferation is evidence of invasion into surrounding tissues. Ultimately, interpreting these findings requires careful correlation with a person’s clinical history, symptoms, and other diagnostic tests to arrive at an accurate diagnosis.