Primary and Secondary Immune Responses
1° Immune Response
- Following the first exposure to a foreign antigen, a lag phase occurs in which no antibody is produced, but activated B cells are differentiating into plasma cells. The lag phase can be as short as 2-3 days, but often is longer, sometimes as long as weeks or months.
- The amount of antibody produced is usually relatively low.
- Over time, antibody level declines to the point where it may be undetectable.
- The first antibody produced is manily IgM (although small amounts of IgG are usually also produced).
2° Immune Response
- If a second dose of the same antigen is given days or even years later, an accelerated 2° or anamnestic immune response (IR) occurs. This lag phase is usually very short (e.g. 3 or 4 days) due to the presence of memory cells.
- The amount of antibody produced rises to a high level.
- Antibody level tends to remain high for longer.
- The main type of antibody produced is IgG (although small amounts of IgM are sometimes produced).
Note: The crossmatch attempts to prevent a 2° immune response by detecting any antibody present, and then ensuring that only antigen-negative red cells are transfused. It cannot prevent a 1° immune response because only autologous red cells or red cells from an identical twin will introduce no foreign antigens into a person being transfused.
In blood banking, a 1° immune response doesn't always cause mainly IgM antibody to be produced. Sometimes only IgG antibody can be detected (e.g., for antibodies in the Duffy or Kidd systems). Similarly, a 2° immune response does not always cause mainly IgG antibody to be produced. Sometimes, only IgM antibody is produced (e.g., for antibodies in the MN or Lewis systems).
||Primary and Secondary Immune Responses