Chronic exposure to benzene and lead can lead to deleterious effects on many biological systems including blood and blood-forming organs. As benzene also causes haematotoxicity even in workers exposed to levels below the US permissible occupational exposure limit of 1 part per million, further . These key events modulated by oxidative stress, dysregulation and reduced immunosurveillance, lead to dysregulated immune response. Benzene can directly damage hematopoietic progenitor cells, which in turn could lead to apoptosis or may decrease responsiveness to cytokines and cellular adhesion molecules. They are heavy metals that lodge in the bone marrow and affect the haematopoiesis and as well as immune response.

I appreciate your answer Dr. Emmanuel Ifeanyl Obeagu, but is it possible to provide me with some references about the effect of lead added to gasoline

you can find useful information in the study mentioned below, the links is attached

Article Current Understanding of the Mechanism of Benzene-Induced Le...

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4151491/

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http://www.nature.com/articles/emm201141

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Article Exposure to benzene induces oxidative stress, alters the imm...

Thank you very much Dr. Mosab Nouraldein Mohammed Hamad