Which of the following is a helpful diagnostic test for observing changes in the anatomy of the heart?

A. T cells: T lymphocytes are primarily involved in cell-mediated immunity and are implicated in conditions such as lymphomas and certain leukemias. Multiple myeloma does not originate from T-cell lines. The disease process specifically affects antibody-producing cells rather than cell-mediated immune cells.

B. B cells: Multiple myeloma arises from malignant transformation of B lymphocytes that have differentiated into plasma cells. These abnormal cells produce excessive amounts of a single immunoglobulin, leading to characteristic clinical features. The neoplasm is therefore classified as a disorder of the B-cell lineage.

C. Immature plasma cells: Immature plasma cells are more commonly associated with plasma cell leukemia or early precursor disorders. Multiple myeloma involves clonal proliferation of plasma cells that are typically mature rather than immature. The disease reflects abnormal antibody production rather than early cell precursors.

D. Mature red blood cells: Mature red blood cells are responsible for oxygen transport and are not involved in neoplastic immune disorders. While anemia may occur as a complication of multiple myeloma, erythrocytes are not the malignant cell type. They are affected secondarily due to marrow infiltration.

Tuberculosis (TB) infection can remain latent, meaning the bacteria are present in the body but inactive. In this dormant state, the individual does not show symptoms and is not contagious, yet the bacteria can reactivate if immunity declines. Latent TB infection is controlled by the immune system, which walls off the Mycobacterium tuberculosis in granulomas. This containment can persist for decades, preventing progression to active disease.