Plasma cell

White blood cells (leukocytes)

Figure 15.4 Blood and Lymphoid Cells All these types of cells are derived from precursor stem cells found in the bone marrow. Some of the steps not yet clearly defined are indicated by dotted arrows. Multiple steps occur between the stem cell and the final cells produced.The role of these cells in the immune response will be explained in this chapter and chapter 16.

Mononuclear Phagocytes

Two functional types of mononuclear phagocytes, macrophages and dendritic cells, arise from the same precursor, the monocyte. Characteristics of mononuclear phagocytes are described here:

■ Monocytes circulate in blood after leaving the bone marrow. When they migrate into tissues they develop into either macrophages or dendritic cells.

■ Macrophages, like neutrophils, are professional phagocytes. Although macrophages are present in

Nester-Anderson-Roberts: Microbiology, A Human Perspective, Fourth Edition

III. Microorganisms and Humans

15. The Innate Immune Response

© The McGraw-H Companies, 2003

378 Chapter 15 The Innate Immune Response

Table 15.2 Human Leukocytes

Cell Type (% of Blood Leukocytes)


Location in body



Neutrophils (polymorphonuclear neutrophilic leukocytes or PMNs, often called polys; 55%-65%)

Mononuclear Phagocytes


Dendritic cells


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