2 Material and Methods
3.2 KIR expression pattern in primates
3.2.1 General characterisation of rhesus macaque lymphocytes using flow cytometry
FITC. No proper labelling could be performed with DyLight405 (data not shown).
Therefore, most of the experiments were performed using the anti‐rhesus macaque KIR antibodies in the APC channel (DyLight633) of the flow cytometer.
3.2 KIR expression pattern in primates
A lot is known about the expression pattern of KIR molecules on different lymphocyte subsets in humans. However, the rhesus macaque as important animal model is not well studied for the expression of these receptors so far. There are studies analysing the expression level of KIR mRNA (Bostik et al., 2009; Moreland et al., 2011) but not the protein expression, due to the absence of specific anti‐rhesus macaque KIR antibodies and lack of cross reactivity of anti‐human KIR antibodies with rhesus macaque KIR proteins.
The characterisation of monoclonal anti‐rhesus macaque KIR antibodies (3.1) was followed by their application to analyse the KIR expression on lymphocyte subsets of rhesus macaques with purified and fluorochrome‐labelled antibodies in multi‐colour flow cytometry. Eight animals were analysed for their KIR expression on NK cells and different T cell subsets like CD8+, CD4+ αβ T cells and γδ T cells. For all animals the KIR genotype was known and the frequency of transcript level was analysed as described by Moreland and colleagues, 2011 (KIR transcript genotyping performed by Christina Albrecht).
3.2.1 General characterisation of rhesus macaque lymphocytes using flow cytometry
Rhesus macaque PBMC are similar to human PBMC, therefore, it is possible to use the same markers for most of the surface molecules to characterise specific cell populations. All non‐KIR antibodies used here were established for human cell surface markers but it was already shown that they also cross‐react with corresponding rhesus macaque proteins (Mavilio et al., 2005). For all analysed PBMC samples of this work the following gating strategy was applied (Figure 13).
First, all doublets were excluded using the FSC‐H against FSC‐A (Monettes),
remaining monocytes by using a CD14 antibody (Lymphoctes exact) and further analysed with CD20 (B cells) and CD3 (T cells) to exclude the CD20+ B cells (Figure 13a).
To characterise the NK cells and different T cell subsets the remaining CD20‐ and CD14‐ population was used.
NK cells of rhesus macaques express only small amounts of CD56 on their surface (around 2 % of all NK cells are CD56+, Webster and Johnson, 2005) so that the traditional human NK marker CD56 is not the appropriate marker for the characterisation of rhesus NK cells. However, nearly all rhesus macaque NK cells express NKG2A (around 97 %, Mavilio et al., 2005). Therefore, NKG2A was used as standard marker for the analysis of rhesus macaque NK cells in this work. All NK cells are also CD8 positive and most express CD16, so these markers were used in combination with NKG2A. Myeloid dendritic cells (mDC) also express CD16 in rhesus macaques. Because of this, all CD16 positive cells had to be further analysed by gating these cells with CD16 against CD8 to exclude the CD8 negative mDCs (CD16 exact population). After these gating steps a Boolean gate was generated with the NKG2A positive population and the CD16 exact population and these cells were defined as NK cells (Figure 13b).
Different T cell subsets were analysed like it is done for the human system using CD4, CD8 and γδ‐TCR (Figure 13c).
As a result of the analysis rhesus macaque lymphocytes have a similar composition as human lymphocytes. There are between 3‐15 % NK cells and 30‐70 % of all lymphocytes are T cells. 37‐75 % are CD4+ αβ T cells, 17‐47 % of all T cells are CD8+ αβ T cells and 2‐15 % express the γδ TCR (Figure 13d).
Figure 13. Characterisation of rhesus macaque PBMC using multi‐colour flow cytometry.
(a) Gating to exclude doublets, granulocytes (size), monocytes (CD14) and B cells (CD20). (b) NK cell gating using NKG2A and CD16 as markers. CD16 positive cells are additionally analysed against CD8 to exclude mDCs. All NKG2A and/or CD16 positive cells were combined using a Boolean gate. (c) T cell gating using CD4, CD8 and γδ TCR antibodies. (d) Overview of the percentage of all analysed lymphocyte populations. Shown is always the percentage of the parental population. The mean
Human NK cells express KIRs in a clonal pattern, i.e. each individual NK cell can express a unique set of KIR and the KIR expression differs between individuals. So far, for rhesus macaques it was not possible to characterise the KIR expression due to the lack of antibodies. Here, NK cells were analysed for their KIR expression by flow cytometry using pan‐KIR antibody 1C7, which recognises all tested KIR (3.1.5). The antibody was labelled with DyLight633 for all experiments shown in this chapter. The already described NK cell population (chapter 3.2.1) was analysed for its KIR expression as it is shown as dot plots for four animals (Figure 14a). Figure 14b summarises the percentage of KIR‐expressing NK cells for 8 different animals. Most of the animals were analysed for more than three times and the mean of the percentage of these experiments is shown in this chart. The KIR expression over time was very constant for healthy individuals e.g. Gerdi (51.80‐55.7 %) or Happy (85.3‐85.7 %) (Figure 36). Further, animals differ in their percentage of KIR‐expressing NK cells (30‐80 %) and also in density, which is defined by the mean fluorescence intensity of KIR expression by these NK cells (Figure 14c). Some animals have many KIR‐expressing NK cells but the density of the expressed KIR is very low per cell, for example for Kalle (80 % KIR positive NK cells, low MFI). The opposite of this is Benno where 50 % of all NK cells express KIR but with the highest density of all animals (Figure 14 b/c).
In conclusion, the frequency of KIR‐expressing NK cells as well as the amount of expressed KIR on NK cells differ between animals. There is no clear correlation between the number of KIR‐expressing NK cells and the density of expressed KIRs (Pearson r=0.3409, p=0.4086).
Figure 14. Flow cytometry analysis of expression of KIR by NK cells.
Antibody 1C7 with a broad KIR reactivity (pan‐KIR) was used. (a) NK cell dot plot examples of different animals using the pan‐KIR antibody are depicted. Gates for KIR positive cells were defined referring to the control without anti‐KIR antibody. (b) Comparison of the percentage of KIR positive NK cells and (c) mean fluorescence intensity (MFI) using 1C7‐DyLight633 are shown.