Recently, the long-term immunological effects of photodynamic therapy have attracted much attention. PDT induced
immune response was mainly initiated through necrotic cells and apoptotic cells, as well as immune cells such as
macrophages. Nitric oxide (NO) as an important regulatory factor in signal transfer between cells has been wildly
studied for generation, development, and metastasis of tumors. NO synthase is a key enzyme in nitric oxide synthesis.
However, inducible nitric oxide synthase (iNOS) is usually activated under pathological conditions, such as stress and
cancer, which can produce high levels of nitric oxide and contribute to tumor cytotoxicity. In addition, increased NO
production by iNOS has been associated with the host immune response and cell apoptosis, which play an important role
in many carcinogenesis and anti-carcinoma mechanisms. This study focuses on the NO production in macrophages,
induced by mouse breast carcinoma apoptotic cells treated by PDT in vitro, and on the effects of immune response
induced by apoptotic cells in tumor cells growth.