Some antibodies against foreign antigens can react to similar self-antigens, causing an autoimmune disease.

A. No:This is incorrect because type AB blood has antigens present on the surface of red blood cells. “No” antigens are characteristic of type O blood, not AB.

B. Anti-A and anti-B:Anti-A and anti-B are antibodies found in the plasma, not antigens on the RBCs. Type AB blood does not have these antibodies, which is why it is the universal recipient.

C. Anti-A:Anti-A is an antibody against A antigens, not an RBC surface antigen. Type AB blood does not produce anti-A antibodies because it naturally expresses A antigens.

D. Anti-B:Anti-B is an antibody against B antigens, also not present on the RBC surface. Type AB blood expresses B antigens, so it cannot have anti-B antibodies.

E. A and B:Type AB blood has both A and B antigens on the red blood cell surface. This dual expression explains why the individual does not produce anti-A or anti-B antibodies, allowing them to receive blood from any ABO type.

A. Weeks:Memory T cells persist far longer than a few weeks. While effector T cells die off quickly after an immune response, memory T cells are designed for long-term immunity rather than short-term survival.

B. Days:A lifespan of only days reflects the behavior of effector T cells during an acute response. Memory T cells, however, undergo homeostatic proliferation and survive well beyond this timeframe.

C. Months:Although memory T cells can certainly survive for months, this does not represent their full potential lifespan. They are known to persist long after the initial antigen exposure.

D. Years:Many memory T cells do survive for years, providing extended protection. However, in humans, the lifespan of memory T cells can surpass even this range, especially after certain viral infections.

E. Decades:Memory T cells can remain functional for decades, offering long-term immunity. Memory T cells from childhood infections can persist into old age, highlighting their exceptional longevity