Effects of strain, sex and age on immunophenotyping parameters in the rat and mouse

Review of immunological plasma markers for longitudinal analysis of inflammation and infection in rat models

Disease or trauma of orthopedic tissues, including osteomyelitis, osteoporosis, arthritis, and fracture, results in a complex immune response, leading to a change in the concentration and milieu of immunological cells and proteins in the blood. While C-reactive protein levels and white blood cell counts are used to track inflammation and infection clinically, controlled longitudinal studies of disease/injury progression are limited. Thus, the use of clinically-relevant animal models can enable a more in-depth understanding of disease/injury progression and treatment efficacy. Though longitudinal tracking of immunological markers has been performed in rat models of various inflammatory and infectious diseases, currently there is no consensus on which markers are sensitive and reliable for tracking levels of inflammation and/or infection. Here, we discuss the blood markers that are most consistent with other outcome measures of the immune response in the rat, by reviewing their utility for longitudinal tracking of infection and/or inflammation in the following types of models: localized inflammation/arthritis, injury, infection, and injury + infection. While cytokines and acute phase proteins such as haptoglobin, fibrinogen, and α₂ -macroglobulin demonstrate utility for tracking immunological response in many inflammation and infection models, there is likely not a singular superior marker for all rat models. Instead, longitudinal characterization of these models may benefit from evaluation of a collection of cytokines and/or acute phase proteins. Identification of immunological plasma markers indicative of the progression of a pathology will allow for the refinement of animal models for understanding, diagnosing, and treating inflammatory and infectious diseases of orthopedic tissues.

Immunohistochemical Characterization of Proliferative Lesions in the Thymus of Aging CD-1 Mice From Two Studies on the RITA Database, With Special Reference to the Perivascular Space

Thymic lymphoid hyperplasia is a common age-related finding, which occurs particularly in female CD-1 mice. The main differential diagnoses are malignant lymphoma and thymoma. A systematic investigation of control groups from two carcinogenicity studies was performed including measurements of thymic size, and the immunohistochemistry (IHC) markers pan-Cytokeratin (pan-CK) for thymic epithelial cells; CD3 and CD45R/B220 for T and B lymphocytes, respectively; CD31 for endothelial cells; and F4/80 for macrophages. Thymoma can be differentiated by increased numbers of proliferating epithelial cells demonstrated by pan-CK IHC staining. Differentiation between lymphoid hyperplasia and lymphoma is more challenging as a mixture of B and T lymphocytes can be present in both findings. The present investigation showed that the thymic perivascular space is the compartment where the increased numbers of lymphocytes in hyperplasia are localized and not the medulla, as previously thought. The lymphoepithelial compartment is atrophic to the same extent in thymi diagnosed with age-related involution or lymphoid hyperplasia. Both diagnoses are thus related to variations in lymphoid cellularity of the nonepithelial perivascular space, which is continuous with the perithymic tissue. Likewise, lymphomas have a predilection to colonize the perivascular space and to spare the lymphoepithelial compartment.

Sex-specific remodeling of T-cell compartment with aging: Implications for rat susceptibility to central nervous system autoimmune diseases

The incidence of multiple sclerosis (MS) and susceptibility of animals to experimental autoimmune encephalomyelitis (EAE), the most commonly used experimental model of MS, decrease with aging. Generally, autoimmune diseases develop as the ultimate outcome of an imbalance between damaging immune responses against self and regulatory immune responses (keeping the former under control). Thus, in this review the age-related changes possibly underlying this balance were discussed. Specifically, considering the central role of T cells in MS/EAE, the impact of aging on overall functional capacity (reflecting both overall count and individual functional cell properties) of self-reactive conventional T cells (Tcons) and FoxP3+ regulatory T cells (Tregs), as the most potent immunoregulatory/suppressive cells, was analyzed, as well. The analysis encompasses three distinct compartments: thymus (the primary lymphoid organ responsible for the elimination of self-reactive T cells - negative selection and the generation of Tregs, compensating for imperfections of the negative selection), peripheral blood/lymphoid tissues ("afferent" compartment), and brain/spinal cord tissues ("target" compartment). Given that the incidence of MS and susceptibility of animals to EAE are greater in women/females than in age-matched men/males, sex as independent variable was also considered. In conclusion, with aging, sex-specific alterations in the balance of self-reactive Tcons/Tregs are likely to occur not only in the thymus/"afferent" compartment, but also in the "target" compartment, reflecting multifaceted changes in both T-cell types. Their in depth understanding is important not only for envisaging effects of aging, but also for designing interventions to slow-down aging without any adverse effect on incidence of autoimmune diseases.

Current Concepts in Natural Killer Cell Biology and Application to Drug Safety Assessments

Natural killer (NK) cells are lymphocytes capable of cytotoxicity against virally infected cells and tumor cells. The display of effector function by NK cells is the result of interactions between germline encoded activating/inhibitory NK cell receptors and their ligands (major histocompatibility complex class I, major histocompatibility complex class I-like, viral, and cellular stress-related surface molecules) expressed on target cells. Determination of NK cell number and function is a common element of the immunotoxicology assessment paradigm for the development of certain classes of pharmaceuticals across a range of modalities. This article summarizes the evidence associating NK cell dysfunction with infectious and cancer risks, reviews emerging NK cell biology, including the impact of immunogenetics on NK cell education and function, and provides perspectives about points to consider when assessing NK cell function in different species in the context of safety assessment.