No abstract

27Natural killer (NK) cells are usually identified by the absence of other lineage markers, 28 due to the lack of a cell surface specific marker. CD56 neg NK cells, classically identified 29 as CD56 neg CD16 + are known to be expanded in some pathological conditions. However, 30 studies on CD56 neg NK cells had revealed different results regarding the phenotype and 31 functionality of these cells. This could be due to, among others, the unstable expression 32 of CD16, which hinders CD56 neg NK cells identification. Hence, we aim to determine 33 an alternative surface marker to CD16 to better identify CD56 neg NK cells. Using 34 multiparametric flow cytometry, we have found that NKp80 is a good alternative to 35 CD16 not only in healthy donors but also in HIV-1 infected subjects and multiple 36 myeloma patients. Furthermore, we found differences between the functionality of 37 CD56 neg NKp80 + and CD56 neg CD16 + NK cells both in healthy donors and patients, 38suggesting that the effector functions of CD56 neg NK cells are not as diminished as 39 previously thought. We proposed NKp80 as a noteworthy marker to identify and 40 accurately re-characterize human CD56 neg NK cells. 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 Keywords: CD16 / CD56negative / HIV / NKp80 / NK cells 56 57 58Natural killer (NK) cells constitute an essential part of the innate immune system, and 59 they are able to eliminate virus-infected and tumor cells without previous 60 sensitization [1,2]. Based on the expression of CD56 and CD16, and the absence of 61 CD3, three NK cell subsets can be distinguish: CD56 bright CD16 +/-, CD56 dim CD16 + and 62 CD56 neg CD16 + . The latter is very scarce in healthy donors, but it is expanded in chronic 63 viral infections, such as HIV-1[3-6]. However, studies with similar cohorts of patients 64 differ in the frequency, functionality and phenotype of the CD56 neg NK cell subset, 65 which could be due to different CD56 neg NK cell identification strategies [7][8][9][10]. 66 Furthermore, it is known that CD16 is downregulated by cryopreservation[11], after 67 cytokine activation and target cell stimulation [12,13]. Thus, the usage of this marker 68 could lead to an inaccurate identification of CD56 neg NK cells and therefore inconsistent 69 results. 71NKp80 is an activating receptor expressed by virtually all fresh and activated mature 72 NK cells [14]. NKp80 marks a critical step in NK cell development [15] and is a NK 73 cell-specific marker among human innate lymphoid cells (ILCs) [16]. However, as far as 74 we know, the possibility of using this marker to better identify CD56 neg NK cells has 75 not been yet explored. 76 77 RESULTS AND DISCUSSION 78 79The CD16 receptor has traditionally been used, in combination with CD56, to identify 80 the three major subsets of NK cells, with CD56 neg NK cells defined as CD56 neg CD16 + . 81However, CD16 is known to be downregulated in some situations, such as, 82 cryopreservation, after cytokine activation and target cell stimulation [11][12][13]. With ...