When a disease-causing agent enters an organism, the immune system alerts which specialized cells? red blood cells epithelial cells white blood cells somatic stem cells

The right answer is white blood cells.

Leukocytes (white blood cells) are an important link in the protection against infections. Indeed, by acting sequentially, they allow the elimination of many foreign agents among viruses, bacteria, fungi and parasites. There are two main categories of cells from a functional point of view, the leucocytes of innate immunity and the leucocytes of adaptive immunity, according to the specificity of non-self recognition.