Adaptive immunity is defined by two important characteristics: specificity and memory. Specificity refers to the adaptive immune system's ability to target specific pathogens, and memory refers to its ability to quickly respond to pathogens to which it has previously been exposed.
___IgD: B. This class of antibody is the first to appear after activation of B cells
___IgM: E. This class of antibody is not secreted by B cells but is expressed on the s...
___IgE: C. This class of antibody is involved in the defense against parasitic infections ...
___IgA: A. This class of antibody is the only one that can cross the placenta