{'fraction_non_alphanumeric': 0.027849740932642485, 'fraction_numerical': 0.02072538860103627, 'mean_word_length': 4.830188679245283, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Characterization of CD4+ T cells in mouse bone marrow. I. Increased activated/memory phenotype and altered TCR Vβ repertoire

A significant proportion of memory B cells home to bone marrow (BM) which is a major site of anamnestic antibody responses in mice. We hypothesized that memory T cells likewise accumulate in BM perhaps to provide help for antibody production and that the compartment of CD4+ T cells in BM of unimmunized mice would be enriched for memory phenotype cells that might have been activated by environmental antigens. The phenotype of activated/memory CD4+ lymphocytes has been defined as CD44hi CD45RBlo CD62L−. Conversely, the phenotype of immunologically naive cells is CD44lo CD45RBhi CD62L+. Flow cytrometric analysis of tissue from normal, adult C57BL/6 mice identified 1‐2  % CD3+CD4+ cells in BM. Up to 40  % of CD3+CD4+ cells in the BM expressed the activated/memory phenotype compared with ≤10  % in the spleen and lymph nodes. Analysis of TCR Vβ repertoire revealed that expression of Vβ3 and Vβ7 genes was increased as much as fourfold in BM compared to the periphery; most of this increase was within the CD44hi T cells. The accumulation of activated/memory T cells and clonotypic expansion(s) was not seen in the BM of germ‐free mice, indicating that it reflects the history of the animal's exposure to antigens. Finally, immunization of mice which express a transgenic T cell receptor specific for ovalbumin peptide resulted in appearance of antigen‐specific T cells with activated/memory phenotype in the BM.