[Bone marrow-derived CD+34 cells expressing interleukin-5 receptor messenger RNA and asthmatic airway inflammation].

OBJECTIVE: To study the possible role of bone marrow-derived hematopoietic cells expressing CD(34)(+) and IL-5 receptor messenger RNA (IL-5R mRNA(+)) in asthmatic airway inflammation.

METHODS: Balb/c mice were sensitized and challenged by ovalbumin (OVA) to establish the asthmatic model. The control mice were sensitized and exposed to sterile saline. The mice were killed at different time points after challenged by OVA and sterile saline, and bronchoalveolar lavage (BALF), peripheral blood (PB) and bone marrow (BM) were prepared. Eosinophils (EOS) in PB and BALF, and nuclear cells in PB and BM were counted. The percentage of CD(34)(+) cells to nuclear cells (CD(34)(+)%) in PB and BM, and the relative number of CD(34)(+) cells (CD(34)(+)) in PB and BM were calculated by flow cytometry. Immunocytochemistry and in situ hybridization were used to observe the hematopoietic cells with co-localized expression of CD34 and IL-5R mRNA (CD(34)(+)/IL-5R mRNA(+)) in BM. The percentage of BM CD(34)(+)/IL-5R mRNA(+) to BM CD(34)(+) was calculated.

RESULTS: (1) At 6 h after OVA challenge, the number of BALF EOS [(2.67 +/- 1.00) x 105/L] was significantly increased as compared to the number in controls [(0.46 +/- 0.06) x 105/L] (P < 0.01). At 12 h after OVA-challenge, the numbers of BALF EOS [(7.74 +/- 1.98) x 105/L] and PB EOS [(2.91 +/- 0.64) x 108/L] were significantly higher than those in the controls (P < 0.01). At 24 h after OVA-challenge, the numbers of BALF EOS[(19.43 +/- 3.69) x 105/L], PB EOS[(3.93 +/- 0.51) x 108/L] and BM CD(34)(+)/IL-5R mRNA(+) [(300.50 +/- 90.02) per thousand] were increased to the highest levels. The differences were significant as compared to the corresponding parameters in the controls (P < 0.01). At 48 h after OVA-challenge, the numbers of BALF EOS [(12.05 +/- 5.31) x 105/L] and BM CD(34)(+)/IL-5R mRNA(+) [(220.80 +/- 53.41) per thousand] were decreased, but were still significantly different compared to the numbers in the controls (P < 0.01), while other markers returned to the normal levels. (2) The number of BM CD(34)(+)/IL-5R mRNA(+) in the 60 mice was closely correlated with BALF EOS, PB EOS, BM CD(34)(+) and BM CD(34)(+) (P < 0.05).

CONCLUSION: CD(34)(+) cells expressing IL-5R mRNA, which may favor eosinophilopoiesis and eosinophilic airway inflammation, were increased in the BM of this mouse asthmatic model. A feedback mechanism between the lungs and the bone marrow likely exists, which may be involved in the development and persistence of asthmatic airway inflammation.