Neonatal calves are highly susceptible to a number of diseases including those that infect via the mucosal surfaces of the respiratory and gastrointestinal tracts. In order to determine appropriate vaccine design and delivery systems, or to identify suitable immunostimulatory methods to combat these infections, a detailed understanding of the immune cell populations present at clinically relevant sites is key.

Few studies have assessed the immune cell composition of the neonatal calf lung and comparisons with circulating immune cells in the blood are lacking. We describe immune cell populations present in the peripheral blood, bronchoalveolar lavage (BAL) fluid and lung tissue of young disease-free calves. Flow cytometric analysis revealed significant differences in cell subset distribution between the peripheral blood and respiratory tract, and between compartments within the respiratory tract. Notably, whereas WC1⁺ γδ TCR + T lymphocytes dominate the peripheral blood, both the BAL fluid and lung tissue contained a high proportion of myeloid cells which expressed CD14 and CD172a (SIRPα). Very low numbers of tissue myeloid cells expressed MHC Class II in comparison to circulating myeloid cells in the blood. Respiratory tract tissues had low frequencies of CD4+ and CD8 + T lymphocytes, which were significantly lower than in the blood. Differences in the proportion of NKp46+ natural killer cells were also observed between tissue compartments. In order to target vaccines or immunostimulatory therapeutics appropriately, these differences in immune cell populations in tissue compartments should be taken into consideration.

新生小牛极易感染多种疾病，包括那些通过呼吸道和胃肠道粘膜表面感染的疾病。为了确定合适的疫苗设计和递送系统，或确定合适的免疫刺激方法来对抗这些感染，对临床相关位点上存在的免疫细胞群的详细了解是关键。

很少有研究评估新生儿小腿肺的免疫细胞组成，并且缺乏与血液中循环免疫细胞的比较。我们描述了年轻无病犊牛的外周血，支气管肺泡灌洗液和肺组织中存在的免疫细胞群。流式细胞仪分析显示，外周血与呼吸道之间以及呼吸道内各隔室之间的细胞亚群分布存在显着差异。值得注意的是，WC1 ⁺γδTCR + T淋巴细胞在外周血中占主导地位，BAL液和肺组织都含有大量表达CD14和CD172a（SIRPα）的髓样细胞。与血液中循环的髓样细胞相比，极少量的组织髓样细胞表达II类MHC。呼吸道组织的CD4 +和CD8 + T淋巴细胞频率较低，显着低于血液中的频率。在组织区室之间也观察到NKp46 +天然杀伤细胞比例的差异。为了适当地靶向疫苗或免疫刺激疗法，应考虑组织区室中免疫细胞群体的这些差异。