Cell-mediated immunity assessments

Follow-on studies are also recommended as needed. These include determination of potential test article effects on blood or tissue immunophenotypes (by flow cytometry or immunohistochemistry), natural killer cell, macrophage, or neutrophil function, host resistance to infection or tumors, and cell-mediated immunity. The important issue in all of these guidelines is this do not ignore signs of immunotoxicity, and assess these findings when observed. 

Another question is whether an endpoint reflecting the status of CMI should be included in any DIT protocol.1719 For the measurement of CMI, roundtable participants suggested that a validated DTH or T-cell responses to anti-CD3 be evaluated.38 The DTH assay is considered by the NTP as part of the Tier II test panel.3 Although reports indicate that the delayed-type hypersensitivity (DTH) response can be assessed in weanling rats.41 roundtable participants agreed that data are lacking as to whether cell-mediated immune (CMI) assessments in younger animals are feasible.38 Ultimately, the characterization of a validated endpoint which measures CMI, and the determination of whether such an endpoint should be an essential part of a DIT framework remain critical research needs. 

Host-resistance assays can be used to assess the overall immunocompetence of the humoral or cell-mediated immune systems of the test animal (host) to fend off infection with pathogenic microbes, or to resist tumorigenesis and metastasis. These assays are performed entirely in vivo and are dependent on all of the various components of the immune system to be functioning properly. Thus, these assays may be considered to be more biologically relevant than in vitro tests that only assess the function of cells from one source and of one type. Since these assays require that the animal be inoculated with a pathogen or exogenous tumor cell, they cannot be performed as part of a general preclinical toxicity assessment, and are thus classified as Type 2 tests in the revised Redbook. These assays are also included as Tier II tests by the NTP. 

The long-term safety of topical tacrolimus ointment 0.1% for 6-12 months has been assessed in 316 patients with atopic dermatitis (82). The most common adverse effects clearly attributed to tacrolimus were a local burning sensation (47%), pruritus (24%), and erythema (12%) the incidences fell with time. The observed incidence of infections did not exceed the expected incidence in patients with atopic dermatitis, and there were no effects on circulating cell-mediated immunity. 

MDP-derivatives with high (A), intermediate/marginal (B) or absent (C) adjuvant activity (as assessed by induction of manifestations of cell-mediated immunity by MDP-supplemented antigen-water-in-oil emulsions in guinea pigs). 

The accepted indications for delayed hypersensitivity skin testing include evaluation of immune disorders or chronic diseases that cause cellular immune dysfunction (e.g., uremia, cancer, AIDS, etc), exposure to infectious pathogens (e.g., Mycobacterium tuberculosis), evaluation of nutritional status (because malnutrition can result in cell-mediated immune deficiency), and in some cases, assessment of immune senescence. 

Cellular immunity protects against intracellular bacteria, viruses and cancer, and is mediated by antigen-specific memory T lymphocytes. DTH is a measure of cellular immunity that relies on the generation of antigen (Ag)-specific memory T cells, which upon subsequent encounter with Ag, become activated, release inflammatory mediators, migrate, and recruit other cell types to the site of contact. The result is an inflammatory reaction and tissue injury. DTH can only be transferred from sensitized to normal individuals via lymphocytes (thus ce//-mediated), not humorally (Ig-mediated), and often takes several days to develop. Thus, the study of DTH (as a follow-on when the weight-of-evidence review indicates additional immunotoxicity studies are warranted) in nonclinical immunotoxicity risk assessment can be a useful predictor of effects on cell-mediated immunity. 

Histoplasmin, a histoplasma capsulatum antigen (0.1 mLof 1 100 dilntion interdermally 5 to 10 cm apart into the volar surface of the forearm) is used to assess cell-mediated immunity and in suspected histoplasmosis. 

Mumps antigen is used to assess cell-mediated immunity. 

Immunotoxicity. The results from the available human and animal studies indicate that di- -butyl phthalate is not a skin-sensitizing agent following dermal exposure (Lehman 1955 Schulsinger and Mollgaard 1980). These studies did not assess other aspects of immunotoxicity. Additionally, immunotoxicity has not been adequately assessed following inhalation or oral exposure. Tests of several additional end points of humoral and cell-mediated immune function are needed to assess the sensitivity of this system to di- -butyl phthalate. 

Unlike types I, 11, and III hypersensitivities, which are mediated by antibodies, delayed or cell-mediated hypersensitivity, classified as type rv, is mediated by antigen-specific effector T cells and this means that the hypersensitivity response can be transferred by purified T cells or a cloned T cell line. Again in contrast to an immediate reaction, a delayed-type hypersensitivity reaction develops over a period of 24-72 h. Delayed hypersensitivity responses have been used for many years to assess patients cell-mediated immunity by the induction of induration and erythema 48-72 h after intradermal injection of so-called recall antigens from Mycobacterium tuberculosis, Candida and Trichophyton species, and tetanus toxoid. 

The effects of a supplement of vitamin Bg on the development of tumors and on the in vitro response associated with cell-mediated immunity were assessed. It was found that peripheral blood and splenic lymphocyte proliferative responses to T cell mitogens such as phytohemagglutinin and concanavaUn A were higher in mice fed the highest levels of pyridoxine. High intake of vitamin Bg also suppressed tumor development (73). 

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