Which one of the following is the middle section of the small intestine:

Intrinsic factor in digestion is a stomach secretion needed for absorption of __________ from the small intestine.

Leukopenia is BEST described as ______________________________?

In which of these situations could virulence of a pathogen in humans be expected to be a coincidence and not an adaptive trait?

Approximately how many HLA-B alleles are currently known from the entire human population?

What is an appropriate definition of antigenic shift in influenza virus?

Which of the nodes corresponds to the most recent common ancestor of humans and frogs?

How many amino acids are typically in the peptides (antigens) that are presented by MHC proteins on cell surfaces?

Antigenic shift can best be described as:

Vaccines function based on the concept of immunological memory.