The invention belongs to the technical field of immunology and relates to a peptide fragment of toxoplasma gondii derived antigen molecule-toxoplasma gondii microneme protein (TgMIC3) for increasing Ly6C+ macrophages as well as application of the peptide fragment. The peptide fragment is named MIC3 and has a sequence shown in SEQ ID NO.2. The invention further discloses the application of the peptide fragment in preparation of the antigen for increasing the Ly6C+ macrophages as well as application of the peptide fragment as an immunoenhancement for enhancing macrophage inflammation response and in preparation of a drug for treating infectious diseases. The peptide fragment MIC3 has broad application prospects in preparation of drugs and preparations for treating infectious diseases.