What is the main feature of chemotaxis as observed in white blood cells?

Chemotaxis is defined as unidirectional movement of leukocytes up a concentration gradient of chemotactic molecules. All granulocytes, monocytes and to a lesser extent lymphocytes respond to chemotactic stimuli with varying rates of speed. Chemoattractants are exogenous or endogenous in nature. Exogenous agents are bacterial products. Endogenous mediators are:Components of complement pathway C5aProducts of lipoxygenase pathway LTB4Cytokines paicularly those of chemokine familyRef: Robbins Pathologic Basis of Disease, 6th Edition, Page 61