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There were two main goals: (1) to evaluate whether workers with a moderately increased PCDD/PCDF -body burden [25-140 ppt TCDD or 104-522 ppt I-TE in blood fat ] exhibit changes in the surface receptors of white blood cells , as observed in previous studies in non-human primates , and (2) to clarify whether persons at the upper range [10-23 ppt TCDD or 30-90 ppt I-TE in blood fat ] of the body burden reference values of a not particularly exposed population show detectable deviations in these immunological variables , when compared with persons at the lower and medium range [1-3 ppt TCDD or 9-29 ppt I-TE ] of these body burden reference values .
 surface receptors, white blood cells
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 surface receptors, white blood cells