PRINCIPLES OF TOXICOLOGY

94 HEMATOTOXICITY: CHEMICALLY INDUCED TOXICITY OF THE BLOOD
phage engulfs (phagocytizes) the particle or foreign cell, and enzymatic processes within these cells
facilitate the digestion of the engulfed particle. Eosinophils provide protection against infectious
organisms by releasing proteolytic enzymes and active oxygen and conducting phagocytotic activities.
An increased number of eosinophils in the blood and tissue is normally observed in allergic (atopic)
individuals who suffer from chronic hay fever or asthma. However, in certain toxicities, such as the
L-tryptophan eosinophilia myalgia syndrome (LTEMS), eosinophil excess resulted from contaminants
that were present an over-the-counter amino acid sleep aid. In this case, the increase in eosinophils
constituted a harmful autoimmune response. Basophils, when stimulated, release histamine, proteolytic
enzymes, and inflammatory mediators. Toxicities involving basophils are almost non-existent.
4.4 THE LYMPHOID SERIES: LYMPHOCYTES (B AND T CELLS)
The lymphoid series gives rise to cells involved in both humoral (B cells) and cellular (T cells)
immunity. B cells function to produce antibodies, while T cells kill virus-infected cells and mediate
the actions of other white blood cells. In the last 15–20 years (at the time of writing), considerable
progress has been made toward understanding (1) the various types of T cells and how they differ in
Figure 4.2 Thymic Maturation of T-Lymphocytes. Immature T-lymphocytes pass through the various layers and
cavities of the thymus gland while acquiring specific functional capabilities. These capabilities result, in part, from
the acquisition of receptors expressed on the cell surface of the T-lymphocytes. T-lymphocytes are identified by the
phenotype expression of specific receptors such as T-suppressor cells which express the CD8 receptor while not
expressing the CD4 receptor. Conversely, T-helper cells are defined by expression of the CD4 receptor protein while
lacking CD8 expression.