L group, thus resulting in the exclusion of all but the two most stable genes in each case.Statistical analysisStudent’s t-test was used for statistical analysis to assess significant differences in qPCR assays. A P value,0.05 was considered to be statistically significant.Results The expression levels of candidate reference genes in tissuesEight housekeeping genes were chosen as reference genes: GAPDH, ACTB, rRNA, B2M, UBC, HPRT, SDHA and TBP. We determined the 
transcription levels of these eight genes in 13 tissues (leukocyte, spleen, lymph node, jejunum, ileum, colon, cerebrum, cerebellum, brainstem, heart, lung, liver and kidney) from four individual common marmosets by qPCR. The sequences of primers specific for each reference gene 
are shown in Table 1. The expression level of each gene in each tissue is shown as the copy number per mg of purified total RNA (Figure 1). The most abundant gene was rRNA while the rarest gene was UBC and the difference in expression level between the two genes was more than 100,000-fold. For several genes, the expression levels were highly different among tissues. For example, B2M expression in heart and brain segments (cerebrum, cerebellum and brainstem) was markedly lower than in other tissues. HPRT expression also showed a large variability among tissues. In addition, the expression levels of rRNA, B2M and HPRT varied among individuals; the mean values of standard deviation were 0.224, 0.235 and 0.303, respectively, while those of the other genes were below 0.2.Flow cytometryHeparinized peripheral blood was collected from common marmosets and centrifuged in Lymphocepal (IBL Co. Takasaki, Japan) at 2,000 rpm for 30 min. Mononuclear cells were collected and re-suspended in RPMI1640 medium containing 10 fetal calf serum. Cells were stained with anti-common marmoset CD8 antibody (Mar8?0) [16] for 15 min at 4uC and washed with 1 (w/v) bovine serum albumin-containing PBS. Subsequently, cells were stained with phycoerythrin-labeled secondary antibody, peridinin chlorophyll protein cyanin5.5 (PerCPCy5.5)-conjugated anti-human CD3 (Sermorelin SP34-2) and Alexa488-conjugated anti-common marmoset CD4 (Mar4-33) antibodies [16]. Peripheral blood from healthy human volunteers was collected and mononuclear cells isolated by Ficoll-Paque (GE Healthcare Biosciences, Uppsala, Sweden) gradient centrifugation. The monoclonal antibodies used for cell staining were as follows: PerCPCy5.5conjugated anti-human CD3 (SP34-2), allophycocyanin-conjugated anti-human CD4 (SK3), fluorescein isothiocyanate-conjugated anti-human CD8 (HIT8a) (BD PharMingen). Cells were analyzed by FACSCalibur (Becton Dickinson, Franklin Lakes, NJ, USA).Gene Expressions in Marmoset by Accurate qPCRTable 2. Sequences of qPCR primers for CD markers and cytokines.Target genea) b) 58-49-1 site Species 59-primer sequence -39 ,Product PCR size (bp) efficiency Reference Reverse CCGGATGGGCTCATAGTCTG ——————-GCCTTCTCCCGCTTAGAGAC ————–C—-AGTTTCTCAGGGCCGAGCAG . —G————–GAGTTTTTCTCCGTTGCTGC ——————-TTGCACAAAGGACATGGAGAACAC —T——————-CTTAAGTGAAAGTTTTTGCTTTGAG ————————CTCAGTTGTGTTCTTGGAGGCA ———————150 150 163 162 144 143 166 166 145 145 104 103 79 77 130 132 81 81 134 134 111 112 127 0.865 0.848 0.926 0.907 0.940 0.912 0.942 1.002 0.806 0.780 0.773 0.797 0.910 0.878 0.871 0.860 0.920 0.990 0.970 0.920 0.935 0.900 0.916 0.964 0.838 0.856 0.887 0.817 DQ189218 NM_000733 AF452616 M35160 DQ189217 NM_001768.L group, thus resulting in the exclusion of all but the two most stable genes in each case.Statistical analysisStudent’s t-test was used for statistical analysis to assess significant differences in qPCR assays. A P value,0.05 was considered to be statistically significant.Results The expression levels of candidate reference genes in tissuesEight housekeeping genes were chosen as reference genes: GAPDH, ACTB, rRNA, B2M, UBC, HPRT, SDHA and TBP. We determined the transcription levels of these eight genes in 13 tissues (leukocyte, spleen, lymph node, jejunum, ileum, colon, cerebrum, cerebellum, brainstem, heart, lung, liver and kidney) from four individual common marmosets by qPCR. The sequences of primers specific for each reference gene are shown in Table 1. The expression level of each gene in each tissue is shown as the copy number per mg of purified total RNA (Figure 1). The most abundant gene was rRNA while the rarest gene was UBC and the difference in expression level between the two genes was more than 100,000-fold. For several genes, the expression levels were highly different among tissues. For example, B2M expression in heart and brain segments (cerebrum, cerebellum and brainstem) was markedly lower than in other tissues. HPRT expression also showed a large variability among tissues. In addition, the expression levels of rRNA, B2M and HPRT varied among individuals; the mean values of standard deviation were 0.224, 0.235 and 0.303, respectively, while those of the other genes were below 0.2.Flow cytometryHeparinized peripheral blood was collected from common marmosets and centrifuged in Lymphocepal (IBL Co. Takasaki, Japan) at 2,000 rpm for 30 min. Mononuclear cells were collected and re-suspended in RPMI1640 medium containing 10 fetal calf serum. Cells were stained with anti-common marmoset CD8 antibody (Mar8?0) [16] for 15 min at 4uC and washed with 1 (w/v) bovine serum albumin-containing PBS. Subsequently, cells were stained with phycoerythrin-labeled secondary antibody, peridinin chlorophyll protein cyanin5.5 (PerCPCy5.5)-conjugated anti-human CD3 (SP34-2) and Alexa488-conjugated anti-common marmoset CD4 (Mar4-33) antibodies [16]. Peripheral blood from healthy human volunteers was collected and mononuclear cells isolated by Ficoll-Paque (GE Healthcare Biosciences, Uppsala, Sweden) gradient centrifugation. The monoclonal antibodies used for cell staining were as follows: PerCPCy5.5conjugated anti-human CD3 (SP34-2), allophycocyanin-conjugated anti-human CD4 (SK3), fluorescein isothiocyanate-conjugated anti-human CD8 (HIT8a) (BD PharMingen). Cells were analyzed by FACSCalibur (Becton Dickinson, Franklin Lakes, NJ, USA).Gene Expressions in Marmoset by Accurate qPCRTable 2. Sequences of qPCR primers for CD markers and cytokines.Target genea) b) Species 59-primer sequence -39 ,Product PCR size (bp) efficiency Reference Reverse CCGGATGGGCTCATAGTCTG ——————-GCCTTCTCCCGCTTAGAGAC ————–C—-AGTTTCTCAGGGCCGAGCAG . —G————–GAGTTTTTCTCCGTTGCTGC ——————-TTGCACAAAGGACATGGAGAACAC —T——————-CTTAAGTGAAAGTTTTTGCTTTGAG ————————CTCAGTTGTGTTCTTGGAGGCA ———————150 150 163 162 144 143 166 166 145 145 104 103 79 77 130 132 81 81 134 134 111 112 127 0.865 0.848 0.926 0.907 0.940 0.912 0.942 1.002 0.806 0.780 0.773 0.797 0.910 0.878 0.871 0.860 0.920 0.990 0.970 0.920 0.935 0.900 0.916 0.964 0.838 0.856 0.887 0.817 DQ189218 NM_000733 AF452616 M35160 DQ189217 NM_001768.