Which antigen, recognized by B cells, is considered T-cell independent?

The pneumococcal antigen is recognized by B cells and is classified as T-cell independent. This means that B cells can respond to this antigen without the help of T-helper cells. T-cell independent antigens typically consist of large, repetitive structures such as polysaccharides found on the surface of certain bacteria. When B cells encounter this type of antigen, they can directly recognize and bind to it, leading to B cell activation and subsequent antibody production without requiring T-cell activation. This is particularly important for rapidly mounting an immune response against encapsulated bacteria like Streptococcus pneumoniae (the causative agent of pneumonia), where the presence of the polysaccharide capsule is key to activating B cells effectively.

In contrast, other choices involve different mechanisms or cell types that do not pertain to T-cell independence. For instance, Staphylococcus aureus does elicit a B cell response, but it involves T-cell mediated help for a robust antibody production. Similarly, CD16/CD56 are markers associated with certain immune cells (natural killer cells), and ADA (adenosine deaminase) is an enzyme involved in purine metabolism rather than a specific antigen. Thus, the pneumococcal antigen stands out as a clear example of a T-cell