"A journey is never easy when you travel alone". I am thankful and feel blessed that God has been kind in providing me always good company in my life. This thesis is a result of five and half years of work during which I have been accompanied and supported by many people. It is a pleasant prospect that I now have the opportunity to express my gratitude to all of them.

First and foremost, I would take this opportunity to express my sincere and profound gratitude to my supervisor Dr. (Miss) Suman Gupta, Scientist E-II, Division of Parasitology, CDRI, Lucknow, for her keen interest and constant encouragement throughout my research training. I respect her vast knowledge and vision for the subject which always reflected in this study. I have been lucky to work under her unique guidance that develops a sense of sincerity and self confidence.

My association with Dr. Amogh A. Sahasrabuddhe "Molecular and Structural Biology" Division has been memorable in every sense. During work in the lab, Dr. Amogh A. Sahasrabuddhe has been the guiding light. He is an outstanding person with such immense human qualities, which would be very difficult for me to put in words. He is a sympathetic and principle-centered person. His boundless enthusiasm and integral view on research and his mission of always aiming at 'nothing less than high quality work', has made a deep impression on me. I owe him a lot of gratitude for having shown me this way of research. I am extremely fortunate to have been associated with him. I am really glad and fortunate that I have had the pleasure of working with such an excellent scientist and more so a gem of a person. I really admire you Sir.

I would like to thank and express my regards to Dr. C. M. Gupta, the Ex Director, CDRI, Lucknow for providing the opportunity to work in CDRI and inspiring to work in the field of "Leishmaniasis". My sincere thanks to Dr. R. Tuli, the Director, CDRI, Lucknow for allowing me extra time to complete my thesis. Thanks are due to Dr. V. M. L. Srivastva, the Ex HOD, Division of Parasitology, CDRI for providing me the necessary facilities and suggestions when I joined CDRI. I also express my sincere gratitude to my present HOD, Dr. S. K. Puri for his all kind support and suggestions in my Ph.D work. I am deeply impressed with his style of encouragement and appreciation that helped me a lot.

I am grateful to the scientists of Division of Parasitology, CDRI, Drs. P.K. Murthy, S. Bhattacharya, A. Dude, N. Kaushal, R. Tripathi, K. Srivastava, Mr. Raja Kumar for helping me whenever and wherever required.

I would also like to thank the scientists who taught me during Pre-Ph.D courses and JNU cell Drs. Alka Singh and Drs. Sheela Ghoshal. I am especially thankful to Mr. Shive Ram for all technical help when I joined CDRI.

I wish to express my deep sense of gratitude to Mr. RK Shrivastava and Mr. Radheshyamji for being a source of joy, encouragement and various unconventional helps they provided since I started doing work in the MSB Division. I am also thankful

to all the technical staff of my division for their help in all the official and technical issues.

This I take as an opportunity to thank my lab members Nishi, Mrs. Shraddha, trainees Neetu, Shweta for their supports. This is an especial moment to thank my colleagues/juniors of MSB Division Shantaram, Satish, Prabodh, Ajay, Dipak, Rashmi and Shailedra who made a joyful and excellent working environment in the lab and are in the true sense, the source of any kind of help.

My division seniors, colleagues and juniors gratefully thank are- Drs. Nirja ma'm, Dr. Saurabh, Mr. Rajivlochan, Nasib, Shravan, Satish, Anil, Dr. Shradha, Malaya, Ramesh chandra, Mukesh, Avanish, Ambuj, Prashant, Pragya, Pramod, Santosh, Anuj, Reema.

I would like to thank those who are other than this department but are never felt like- Dr. Anil Gaikwad, Dr. Rit Vatsyayan, Mr Santosh (Biochem.), Dr. Manish (Micro.), Dr. Satyawan (Pharmeceutics), and Dr. Satyanand (Pharmacology), Dr. Naveen, Mr. Devesh (Med. Chem.).

I am very much thankful to my friends Dr. Ramesh, Dr. Sandeep, Pankaj, Dr. Santosh (Birbal Sahani Institute of Paleobotany) for their continuous encouragement and exchanges of valuable ideas and making funny environment.

I wish to extend my thanks and appreciation to people in the library, administration, store, purchase, tissue culture laboratory-Dr. A. K. Balapure, Dr. Ramesh Sharma, FACS section - Mr. A. L. Vishwakarma, animal house-Dr. K. Rai, Mr. Dube, photpgraphy section- Mr. R. M. Pathak, Mr. G. C. Gupta, and Biometry and Statistics Division -Mr. M. P. S. Negi without their support I couldn't achieved this goal. I also thank Mr. Kishan (FT Division) for making equipments sterile timely and my lab attendant Mr. Prem Babu for all kind of support.

I also wish to thank the teachers of my Dean Dayal Upadhyay Gorakhpur Univ., Gorakhpur who belief I can do my best Prof. Kamal (Ex. HOD of Botany) and Dr. Yeshwant Singh (senior reader Depot of Botany).

Financial support in form of fellowships by CSIR is duly acknowledged. Finally, I come to the precious moment of paying my heartfelt and sincere thanks to my family members and relatives. I am extremely thankful to my father (Shri RamPyare) and specially mother (Late Chandrawati Devi) for understanding values of education and giving me freedom to choose my path. Maa, I extremely missed you. Having a real brother one can feel pleasure, enjoy success and exchange many things that could not be shared with any other, the same was with me. During writing this thesis I missed my younger (Mr. Kamlesh) brother in accidental death, I was extremely shocked, felt darkness everywhere but thank to God for giving me patience and praise you to keep his soul in peace. I am missing you a lot at this moment when our dream is coming in reality. Thanks are also to my sisters and Jijas who always caring me. I also thank to my uncles, aunties and cousins for their helps and affections. I am equally obliged to many others whose names I might have inadvertently missed out, for which I am sure I would be forgiven.

Ramesh