Answer:
[tex]\huge\boxed{\sf Endocytosis}[/tex]
Explanation:
B-cells engulf an antigen by endocytosis.
Endocytosis:
The process by which cell takes up external materials by fusing them with plasma membrane is called endocytosis.
After engulfing the antigen, B-cells become sensitive to the pathogen.
[tex]\rule[225]{225}{2}[/tex]
Hope this helped!