What is the relationship between the circulatory system and the immune system?

1) Cells of the immune system use the circulatory system as a medium to patrol the body.
2) Cells of the immune system use the circulatory system to mature.
3) Cells of the immune system use the circulatory system for B-cell activation.
4) Cells of the immune system use the circulatory system for replication.
The answer should be 1 or 4

Image may be NSFW.
Clik here to view.