1. A DNA sequence encoding Tumor Necrosis factor related Ligand, said sequence consisting essentially of SEQ ID NO: 1. 2. A DNA sequence encoding Tumor Necrosis factor related Ligand, said sequence consisting essentially of SEQ ID N0: 3. 3. A DNA molecule encoding a polypeptide, wherein said polypeptide comprises an amino acid sequence that is at least 50% homologous with the active site of Tumor Necrosis Factor Related Ligand, wherein said DNA molecule hybridizes to a DNA probe comprising at least 20 consecutive nucleotides of SEQ ID NO: 1. 4. A DNA molecule encoding a polypeptide, wherein said polypeptide comprises an amino acid sequence that is at least 50% homologous with the active site of Tumor Necrosis Factor Related Ligand, wherein said DNA molecule hybridizes to a DNA probe comprising at least 20 consecutive nucleotides of SEQ ID N0:3. 5. A DNA sequence encoding a Tumor Necrosis Factor Related Ligand, wherein the encoded Tumor Necrosis Factor Related Ligand comprises the amino acid sequence of SEQ ID N0: 2 except that said amino acid sequence comprises conservative substitutions, alterations or deletions. 6. A DNA sequence encoding a Tumor Necrosis Factor Related Ligand, wherein the encoded Tumor Necrosis Factor Related Ligand comprises the amino acid sequence of SEQ ID N0: 4 except that said amino acid sequence comprises conservative substitutions, alterations or deletions. 7. A recombinant DNA molecule comprising a DNA sequence of claim 1, wherein said sequence is operatively linked to an expression control sequence. 8. A recombinant DNA molecule comprising a DNA sequence of claim 2, wherein said sequence is operatively linked to an expression control sequence. 9. A recombinant cell line comprising a DNA molecule of claim 1 or claim 7 for expression of a Tumor Necrosis Factor related Ligand, wherein said cells are selected from EBNA293 cells and High Five(TM) cells. 10. A recombinant cell line comprising a DNA molecule of claim 2 or claim 8 for expression of a Tumor Necrosis Factor related Ligand, wherein said cells are selected from EBNA293 cells and High Five(TM) cells. 11. A Tumor Necrosis Factor Related Ligand comprising a biologically functional sequence comprising the amino acid sequence of SEQ ID NO: 2. 12. A Tumor Necrosis Factor Related Ligand comprising a biologically functional sequence comprising the amino acid sequence of SEQ ID NO: 4. 13. A method for producing a ligand according to claim 11, which comprises culturing host cells of claim 9, under conditions wherein a host cell produces a ligand, and isolating said ligand. 14. A method for producing a ligand according to claim 12, which comprises culturing host cells of claim 10, under conditions wherein a host cell produces a ligand, and isolating said ligand. 15. A Tumor Necrosis Factor Related Ligand comprising the sequence SEQ ID N0: 2 produced by the method of claim 13, wherein said ligand produced in this manner is subsequently purified to a high degree of purity. 16. A Tumor Necrosis Factor Related Ligand comprising the sequence SEQ ID N0: 4 produced by the method of claim 14, wherein said ligand produced in this manner is subsequently purified 10 a high degree of purity. 17. A pharmaceutical composition comprising a therapeutically effective amount of a ligand according to claim 11 and a pharmaceutically acceptable carrier. 18. A pharmaceutical composition comprising a therapeutic ally effective amount of a ligand according to claim 12 and a pharmaceutically acceptable carrier. 19. A method for preventing or reducing the severity of an autoimmune disease, comprising the step of administering to a patient a therapeutically effective amount of the pharmaceutical composition of claim 17. 20. A method for preventing or reducing the severity of an autoimmune disease, comprising the step of administering to a patient a therapeutically effective amount of the pharmaceutical composition of claim 18. 21. A method for preventing or reducing the severity of an immune response to a tissue graft, comprising me step of administering 10 a patient a therapeutically effective amount of the pharmaceutical composition according 10 claim 17. 22. A method for preventing or reducing the seventy of an immune response to a tissue graft, comprising the step of administering to a patient a therapeutically effective amount of the pharmaceutical composition according to claim 18. 23. A method for stimulating the immune system, comprising administering 10 a patient an effective amount of the composition according to claim 17. 24. A method for stimulating the immune system, comprising administering to a patient an effective amount of the composition according to claim 18. 25. A method for suppressing the immune system, comprising administering to a patient an effective amount of the pharmaceutical composition according to claim 17. 26. A method for suppressing the immune system, comprising administering to a patient an effective amount of the pharmaceutical composition according to claim 18. 27. A method for treating cancer, comprising administering to a patient an effective amount of the pharmaceutical composition according to claim 17, 28. A method for treating cancer, comprising administering to a patient an effective amount of the pharmaceutical composition according to claim 17. 29. A method for identifying a molecule that specifically binds to a Tumor Necrosis Factor Related Ligand according to claim 11, said method comprising: (a) providing a biologically-active Tumor Necrosis Factor Related Ligand (b) labeling said biologically-active Tumor Necrosis Factor Related Ligand with a detectable label; (c) contacting a composition comprising at least one protein to a labeled, biologically-active Tumor Necrosis Factor Related Ligand of step (b); (d) detecting specific binding of a protein to said labeled, biologically-active Tumor Necrosis Factor Related Ligand, thereby identifying a molecule that specifically binds to the labeled Tumor Necrosis Factor Related Ligand. 30. A soluble fragment of the Tumor Necrosis Factor Related Ligand of claim 11 wherein said fragment comprises the amino acid sequence of SEQ ID N0: 2 without the transmembrane portion and N-terminus of said Tumor Necrosis Factor Related Ligand. 31. A soluble fragment of the Tumor Necrosis Factor Related Ligand of claim 12 wherein said fragment comprises the amino acid sequence of SEQ ID N0: 4 without the transmembrane portion and N-terminus of said Tumor Necrosis Factor Related Ligand. 32. An analog of a Tumor Necrosis Factor Related Ligand comprising an amino acid sequence that is at least 40% homologous to a polypeptide sequence of SEQ ID N0:2 wherein said analog is encoded by a DNA molecule of claim 3. 33. An analog of a Tumor Necrosis Factor Related Ligand comprising an amino acid sequence that is at least 40% homologous to a polypeptide sequence of SEQ ID N 0:2 wherein said analog is encoded by a DNA molecule of claim 4. 34. A method for producing an antibody preparation reactive to the Tumor Necrosis Factor Related Ligand of claim 11 comprising the step of immunizing an organism with said Tumor Necrosis Factor Related Ligand or an antigenic fragment thereof. 35. A method for producing an antibody preparation reactive to the Tumor Necrosis Factor Related Ligand of claim 12 comprising the step of immunizing an organism with said Tumor Necrosis Factor Related Ligand or an antigenic fragment thereof. 36. An antibody preparation produced by the method according to claim 34. 37. An antibody preparation produced by the method according to claim 35. 38. A pharmaceutical composition comprising an antibody preparation according to claim 36. 39. A pharmaceutical composition comprising an antibody preparation according to claims 37. 40. A method of expressing a gene in a mammalian cell, comprising: (a) introducing a sequence according to claim 1 that encodes a Tumor Necrosis Factor Related Ligand into a cell; (b) allowing said cell to live under conditions such that said gene is expressed in said mammalian cell. 41. A method of expressing a gene in a mammalian cell, comprising: (a) introducing a sequence according to claim 2 that encodes a Tumor Necrosis Factor Related Ligand into a cell; (b) allowing said cell to live under conditions such that said gene is expressed in said mammalian cell. 42. A method of treating a disorder related to Tumor Necrosis Factor Related Ligand, comprising administering an effective amount of a recombinant molecule according to claim 7 into a mammalian cell. 43. A method of treating a disorder related to Tumor Necrosis Factor Related Ligand, comprising administering an effective amount of a recombinant molecule according to claim 8 into a mammalian cell. 44. The method of claims 42 and 43, wherein the mammal is a human being. 45. A method of inducing cell death comprising the administration of an agent capable of interfering with the association of Tumor Necrosis Factor Related Ligand of claim 11 to its receptor, wherein the agent interfering with the association between Tumor Necrosis Factor Related Ligand and its receptor is the soluble Tumor Necrosis Factor Related Ligand of claim 30. 46. A method of inducing cell death comprising the administration of an agent capable of interfering with the association between Tumor Necrosis Factor Related Ligand of claim 12 and us receptor, wherein the agent interfering with the association between Tumor Necrosis Factor Related Ligand and its receptor is the soluble Tumor Necrosis Factor Related Ligand of claim 31. 47. The method according to claims 45 and 46, further comprising the administration of-interferon. 48. A method of treating, suppressing or altering an immune response involving a signaling pathway between Tumor Necrosis Factor Related Ligand and its receptor, said method comprising the administration of an effective amount of an agent capable of interfering with the association between Tumor Necrosis Factor Related Li