PRINCIPLES OF TOXICOLOGY - Biology East Borneo

10.5 TESTS FOR DETECTING IMMUNOTOXICITY IN ANIMAL MODELS 197normally produces cellular proliferation and increased immunoglobulin synthesis. This responserequires both T H and B cells, and provides an indication of the capability of these two cells to interactproperly and of B cells to produce immunoglobulins. Lipopolysaccharide (LPS) is a mitogen effectiveselectively on B cells, while phytohemaglutinin (PHA) and concanavalin A (con A) are selective T-cellmitogens. Other stimulants to lymphocyte activation can be used, such as tetanus toxoid, diptheriatoxoid, Candida, and PPD, if the subject has been previously exposed to these. The rapid cell divisioncharacteristic of a normal response to these mitogens is typically assessed by measuring incorporationof 3 H-thymidine into DNA of the cells. Other endpoints of stimulation, such as increased expressionof IL2 receptors on T cells, can also be evaluated. The results of these tests are particularly prone tovariability, and the tests should be repeated on several occasions in order to demonstrate an abnormalresponse.In the mixed-lymphocyte reaction (MLR) test, lymphocytes from the test subject and anotherindividual are mixed. Normally, contact with the allogenic lymphocytes will cause the test subject’slymphocytes to become activated and proliferate. To conduct this assay, the target lymphocytes arerendered incapable of replication, often by irradiation or by treatment with mitomycin C. Test subjectlymphocytes are then added, and the rate of their replication is evaluated by measuring incorporationof 3 H-thymidine. The cytotoxic lymphocyte (CTL) assay takes the lymphocyte interactions one stepfurther to evaluate the ability of cytotoxic T cells (T C) to destroy target cells. After incubation of thetest subject and target lymphocytes, the subject T Care isolated, washed, and reincubated with targetlymphocytes preloaded with 51 Cr. As the target cells are destroyed, 51 Cr is released into the mediumand can be measured, providing an index of cytotoxic capabilities of the T Clymphocytes.Fluorescent Antinuclear Antibody Assay (FANA) The indirect immunofluorescence antinuclearantibody assay (FANA) may be the initial screening test used to show autoimmunity. However, severalFANA patterns are recognized in various connective-tissue diseases and some low-titer stainingpatterns have also been reported in sera from persons exposed to environmental agents. The followingstaining patterns may be observed:1. The diffuse (homogenous) staining pattern, which is usually associated with antibody directedto DNA-histone or histone subfractions. This staining pattern is frequently found in sera frompatients receiving chronic treatment with procainamide, hydralazine, isoniazid, anticonvulsantdrugs, and some environmental chemical agents.2. A peripheral (rim) pattern, which is attributed to antibody reacting with native DNA andsoluble DNA-histone complexes. This staining pattern is frequently seen in sera from patientswith systemic lupus erythematosus (>95 percent).3. Speckled FANA staining, which is usually attributed to antibodies reacting with saline-solubleantigens. These antibodies are directed to nonhistone antigens and include Sm, ribonucleoprotein,SS-A/Ro, SS-B/La, PM-1, and SCl-70. While these staining patterns frequently occur inpatients with mixed connective tissue diseases, including Sjögren’s syndrome, polymyositisand progressive systemic sclerosis, they have also been found in sera from persons exposed toimmunotoxic agents.4. The nucleolar staining pattern, which has been restricted to antibodies reactive with nucleolarRNA. This pattern is associated with a particular form of systemic sclerosis (progressivesystemic sclerosis).10.5 TESTS FOR DETECTING IMMUNOTOXICITY IN ANIMAL MODELSFor most chemicals, an assessment of their potential to produce immunotoxicity in humans is basedon testing in animals. Many of the tests used in animal studies are the same as, or at least analogousto, those available for clinical assessment described above. However, studies in animals offer the