A method for detecting immunoglobulin light chain restriction and clonality in B cells, the method comprising: (a) conducting one or more in situ hybridization assays on a sample of B cells from a subject using at least one probe set which is designed to specifically hybridize to immunoglobulin kappa chain constant region (IGKCR) RNA; at least one probe set which is designed to specifically hybridize to immunoglobulin lambda chain constant region (IGLCR) RNA; and at least one probe set which is designed to specifically hybridize to immunoglobulin lambda-like polypeptide 5 (IGLL5) RNA; (b) detecting a signal associated with hybridized IGKCR probe, a signal associated with hybridized IGLCR probe and a signal associated with hybridized IGLL5 probe in a population of B cells in the sample; and (c) determining a pattern of the signals associated with hybridized IGKCR probe, hybridized IGLCR probe and hybridized IGLL5 probe within individual cells in the B cell population, wherein the pattern, where both the signal associated with IGKCR probe and the signal associated with IGLCR probe are present in the B cell, and where the level of the signal associated with hybridized IGLL5 probe is greater than or equal to the level of the signal associated with hybridized IGLCR probe, indicates kappa restriction; or the pattern, where both the signal associated with IGKCR probe and the signal associated with IGLCR probe are present in the B cell, and where the level of the signal associated with hybridized IGLL5 probe is less than the level of the signal associated with hybridized IGLCR probe, indicates a non-restricted sample. (a) conducting one or more in situ hybridization assays on a sample of B cells from a subject using at least one probe set which is designed to specifically hybridize to immunoglobulin kappa chain constant region (IGKCR) RNA; at least one probe set which is designed to specifically hybridize to immunoglobulin lambda chain constant region (IGLCR) RNA; and at least one probe set which is designed to specifically hybridize to immunoglobulin lambda-like polypeptide 5 (IGLL5) RNA; (b) detecting a signal associated with hybridized IGKCR probe, a signal associated with hybridized IGLCR probe and a signal associated with hybridized IGLL5 probe in a population of B cells in the sample; and (c) determining a pattern of the signals associated with hybridized IGKCR probe, hybridized IGLCR probe and hybridized IGLL5 probe within individual cells in the B cell population, wherein the pattern, where both the signal associated with IGKCR probe and the signal associated with IGLCR probe are present in the B cell, and where the level of the signal associated with hybridized IGLL5 probe is greater than or equal to the level of the signal associated with hybridized IGLCR probe, indicates kappa restriction; or the pattern, where both the signal associated with IGKCR probe and the signal associated with IGLCR probe are present in the B cell, and where the level of the signal associated with hybridized IGLL5 probe is less than the level of the signal associated with hybridized IGLCR probe, indicates a non-restricted sample. the pattern, where both the signal associated with IGKCR probe and the signal associated with IGLCR probe are present in the B cell, and where the level of the signal associated with hybridized IGLL5 probe is greater than or equal to the level of the signal associated with hybridized IGLCR probe, indicates kappa restriction; or the pattern, where both the signal associated with IGKCR probe and the signal associated with IGLCR probe are present in the B cell, and where the level of the signal associated with hybridized IGLL5 probe is less than the level of the signal associated with hybridized IGLCR probe, indicates a non-restricted sample. <EOS>