Amyloid is insoluble fibrillar protein deposited in the extracellular space. The resulting heterogeneous group of disorders is called amyloidosis. The protein in the fibrils are hydrogen bound intermolecularly in β-sheets giving the fibrils a considerable strength and the structure explains most of the characteristic properties of amyloid. Today, about 25 proteins are known to form amyloid in vivo
and these are involved in life-threatening disorders like type-2 diabetes and Creutzfeldt Jaco
s disease 
The systemic amyloidoses are characterized by widely spread deposits of specific proteins in a characteristic fibrillar form. Usually vital organs are affected and the disorders are therefore often lethal. More than ten different proteins are known to be able to give rise to systemic amyloidosis, most of them in rare, hereditary forms 
. In systemic AL-amyloidosis, the amyloid fibril protein is derived from monoclonal immunoglobulin light chains. All light chain subtypes are capable of fibril formation although lambda chains, particularly of lambda-VI type, are over-represented.
The immunoglobulin light chain in systemic AL-amyloidosis is produced by plasma cells, mainly in the bone marrow. The protein is then circulating in plasma before it aggregates into the typical amyloid fibrils at sites far from the origin. Most commonly it is not the whole protein that is included but the variable region with a part of the constant region. Whether or not this C-terminal cleavage occurs before the assembly and is important in this process or is a result of proteolytic trimming of a part not included in the fibril core is still not known. Usually, full-length light chains are included in the fibril as a minor component 
. On rare occasions, the major fibril protein is derived from the constant region 
Systemic AL-amyloidosis is probably the most heterogeneous form of amyloidosis that occurs. There is no general rule regarding where deposits may occur, which is different from most other systemic amyloidoses. Therefore, the clinical presentation is highly variable. In some patients, cardiac symptoms predominate, in others nephropathy. Again others present with polyneuropathy, gastrointestinal disturbances, liver affection and so on 
. In accordance with the systemic nature of the disease, combinations are common and in reality, most organs are involved also when not giving symptoms. However, amyloid does not occur in the central nervous system 
It has been difficult to explain why only some individuals with production of monoclonal immunoglobulin light chains develop systemic amyloidosis. After an increasing number of amino acid sequences of AL-proteins have been obtained, it has become more clear that some unusual amino acid substitutions or even light chain subgroups 
are over-represented in these proteins. In addition, glycosylation may be linked to AL amyloidogenesis 
. Further studies have given an increasing body of information on the putative importance of certain amino acid substitutions in the AL-protein sequences 
. Thus, it was found that over 80% of amyloidogenic κI variable light chains regions were characterized by the presence of at least one of three single-site amino acid substitutions or formation of an N-linked glycosylation site 
. Consequently, it is increasingly clear that the most important risk factor for the development of AL-amyloidosis is related to the structure (and concentration) of the monoclonal immunoglobulin light chain. Interestingly, at least for κ chains, these risk factors seem to be a random matter, since they may be identified in the normal antibody repertoire 
. Amyloidosis may then be a consequence of a clonal expansion of a plasma cell producing these specific light chains.
The reasons for the variability in organ distribution in systemic AL-amyloidosis are not known. It is reasonable to believe that variations are due to properties related to differences in protein sequences. In addition to differences in properties in the individual light chains, it has been suggested that there is a preferential organ tropism for different variable light chain gene products 
. Thus, AL λVI is significantly more often associated with clinically important renal amyloidosis than other subtypes 
. However, the literature is sparse concerning the nature of the amyloid light chain subgroup and distribution of amyloid in the body. This is in a high degree true for amyloid of AL κ type 
although κI light chains are particularly well represented in immunoglobulin light chain sequences 
. Moreover, performed studies are based on clinical evaluation of effects of amyloid on the organ in whole. Almost no studies on the structure of AL-proteins include any detailed histological analyses, allowing comparisons on how deposits are distributed in specific tissue structures. Finally, studies in which both the AL-protein sequence and the tissue distribution have been determined do not exist.
In the present study we have chosen to study four AL amyloid proteins of κIb type (O18-O8) and, for comparison, four amyloidogenic light chains of L2-L16 origin (κ3a). We have evaluated the distribution of amyloid deposits in the body from available tissues, obtained at autopsy. The use of the material and the study has been approved by the Ethical Committee of the Uppsala University Hospital.