**6. Conclusion**

In conclusion, induction of TLR signaling pathway by infectious pathogen recognition provides a better understanding of innate immune defense mechanism against this disease. Immunotherapy emerges as a promising therapeutic approach for parasitic infection treatment over the past few years. Although no effective drugs have emerged, vaccine adjuvants yield promising results due to induction of cellular immunity via TLR. Large scales of clinical studies were conducted for developing potent and well-tolerated adjuvants. The protozoan and helminth parasites can cause activation (to a small degree) and negative regulation (to a larger degree) of TLRs resulting in increasing or decreasing parasite burden [103]. TLR agonists or antagonists are small molecule mimics, natural ligands used for treating Type I allergy, cancer, and infectious diseases. MF59 (Novartis) and AS04 (GSK) are some examples of TLR4 agonist licensed for human use [124]. GLA (TLR4 ligand) and

3M-052 (TLR7/8) ligands are now in clinical trial. Recently, RTS,S/AS01, a recombinant chimeric protein (c-terminal of circumsporozoite antigen fused with HPB antigen, and "ASO1" refers to the adjuvant formulation MPL and QS21, a natural glucoside), is used for treating Malaria [125]. Several new drugs have been chemically synthesized for better understanding of the interaction of TLRs with their ligands. The knowledge from these studies will provide a greater opportunity for developing plant-derived new therapeutic drugs. So, major efforts are required for targeting TLRs in pathological conditions.
