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Background: There is a growing body of evidence to suggest that CD8+ T lymphocytes contribute to local allergen-induced eosinophilic inflammation. Since bone marrow (BM) responses are intricately involved in the induction of airway eosinophilia, we hypothesized that CD8+ T lymphocytes, as well as CD4+ T lymphocytes, may be involved in this process., Methods: Several approaches were utilized. Firstly, mice overexpressing interleukin-5 (IL-5) in CD3+ T lymphocytes (NJ.1638; CD3IL-5+ mice) were bred with gene knockout mice lacking either CD4+ T lymphocytes (CD4-/-) or CD8+ T lymphocytes (CD8-/-) to produce CD3IL-5+ knockout mice deficient in CD4+ T lymphocytes (CD3IL-5+/CD4-/-) and CD8+ T lymphocytes (CD3IL-5+/CD8-/-), respectively. Secondly, CD3+, CD4+ and CD8+ T lymphocytes from naïve CD3IL-5+ and C57BL/6 mice were adoptively transferred to immunodeficient SCID-bg mice to determine their effect on BM eosinophilia. Thirdly, CD3IL-5+, CD3IL-5+/CD8-/- and CD3IL-5+/CD4-/- mice were sensitized and allergen challenged. Bone marrow and blood samples were collected in all experiments., Results: The number of BM eosinophils was significantly reduced in CD3IL-5+/CD8-/- mice compared to CD3IL-5+ mice and CD3IL-5+/CD4-/- mice. Serum IL-5 was significantly higher in CD3IL-5+/CD4-/- mice compared to CD3IL-5+ mice but there was no difference in serum IL-5 between CD3IL-5+/CD4-/- and CD3IL-5+/CD8-/- mice. Adoptive transfer of CD8+, but not CD4+ T lymphocytes from naïve CD3IL-5+ and C57BL/6 mice restored BM eosinophilia in immunodeficient SCID-bg mice. Additionally, allergen challenged CD3IL-5+/CD8-/- mice developed lower numbers of BM eosinophils compared to CD3IL-5+ mice and CD3IL-5+/CD4-/- mice., Conclusion: This study shows that CD8+ T lymphocytes are intricately involved in the regulation of BM eosinophilopoiesis, both in non-sensitized as well as sensitized and allergen challenged mice.

We evaluated whether bone marrow (BM) inflammatory cells have capacity to traffic into the airways following allergen exposure in a mouse model of allergen-induced airway inflammation. We also evaluated the effect of IL-5 overexpression on (i) the production of eosinophils in BM, (ii) the accumulation of eosinophils, neutrophils and lymphocytes in blood and airways and (iii) the changes in CD34+ cell numbers in BM, blood and airways. Bromodeoxyuridine (BrdU) was used to label cells produced during the exposure period. Furthermore, CD3 splenocytes were adoptively transferred to investigate the BM inflammatory response. Allergen exposure induced traffic of BM eosinophils, neutrophils and lymphocytes to the airways and increased the number of BrdU+ eosinophils, neutrophils, lymphocytes and CD34+ cells in BALf. IL-5 overexpression enhanced the eosinophilopoiesis and increased the presence of BrdU+ eosinophils and CD34+ cells in airways and enhanced the number of CD34+ cells in BM and blood after allergen exposure. Adoptive transfer of CD3 lymphocytes overexpressing IL-5 caused increased BM eosinophilia. In conclusion, allergen exposure induces traffic of not only newly produced eosinophils but also newly produced neutrophils and lymphocytes into the airways.

The aim of this study was to evaluate the effect of a neutralizing anti-interleukin (IL)-5 monoclonal antibody (TRFK-5) on bone marrow and airway CD34(+) and immature eosinophils. A focus was to determine the effect of the timing of treatment. Balb/c mice were ovalbumin-sensitized and subsequently exposed to ovalbumin for 5-10 d via airway route. Animals were treated intraperitoneally with TRFK-5 or its isotype control (50 microg) once at different time points. Newly produced eosinophils were labeled using 5-bromo-2'-deoxyuridine (BrdU). BrdU(+) and CD34(+) eosinophil numbers were examined by immunocytochemistry. TRFK-5 reduced bone marrow immature eosinophils within 3 d. This effect was closely related to a reduction of BrdU(+) and CD34(+) bone marrow eosinophils, and reduced numbers of blood eosinophils. However, bronchoalveolar lavage (BAL) eosinophilia was not attenuated to the same degree. The effect of TRFK-5 was most prominent in the extended allergen-exposure protocol, where the treatment was given in the middle of the exposure, with strongly reduced bone marrow CD34(+) and immature bone marrow eosinophils, blood eosinophils as well as BAL BrdU(+) eosinophils, and BAL CD34(+) eosinophils. These data argue that anti-IL-5 downregulates eosinophilopoiesis within 3 d by action in the bone marrow, by inhibition of the early stages of eosinophil maturation from CD34(+) cells.

We hypothesized that the allergen-induced increased number of airway eosinophils results from increased recruitment of eosinophils from bone marrow (BM) and local development of CD34(+) cells into eosinophils. We also assumed that the phenotype of airway eosinophils depends on whether these cells have differentiated within BM or airway. C57BL/6 mice were sensitized and subsequently exposed to ovalbumin (OVA) on 5 consecutive days. Newly produced cells were labeled with a thymidine analog. Clonogenic activity and interleukin 5 (IL-5) release from bronchoalveolar lavage fluid (BALf) CD34(+) cells were evaluated by using cell-culture techniques. Allergen exposure induces increase in CD135(+) primitive myeloid progenitors within the BM CD34(+) cell population, without significant changes in total number of CD34(+) cells or newly produced CD34(+) cells. CD34(+)/IL-5R alpha(+) cells in the first stage of cell differentiation were found only in BM, arguing that early commitment of CD34(+) cells into the eosinophil lineage is restricted to the BM compartment. Allergen exposure induces a shift in differentiation of BM, blood, and BALf eosinophillineage-committed CD34(+) cells toward mature eosinophils and recruitment of these cells via blood into airway. We further demonstrate in vitro that ability to multiply persists in BALf CD34(+) cells but not CD34(-) cells, likely via autocrine IL-5 release and IL-5-induced up-regulation of IL-5R alpha.