A further consideration relates to variations in antibody

levels in a given individual’s serum samples, collected at different times. The most reactive serum is generally called the ‘peak serum’. This may have been collected selleck products several years earlier, with the ‘current serum’ showing quite different reactivity. As an example, the peak serum may show a clear positive CDC crossmatch result, but as the antibody levels have fallen in subsequent sera, so too may the degree of cell lysis in the assay. This may render the CDC crossmatch negative. Nevertheless, the antibodies found in the peak sera may still be of relevance, increasing the risk of early rejection as a result of this prior sensitization and the resulting immunological memory. For this reason, patients on transplant waiting lists have sera collected at frequent intervals; variations can be monitored

and newly appearing HLA antibodies can be detected. In interpreting crossmatches a basic understanding of HLA expression is required. The genes encoding check details HLA are found on chromosome 6 and are inherited en bloc; such that half of each individual’s HLA (an allele) will be from each parent.9 HLA is divided into class I and class II. Class I molecules are HLA A, B and C while class II molecules are HLA DR, DP and DQ. Class I molecules are expressed on all nucleated cells while class II molecule Progesterone expression is restricted to cells such as antigen presenting cells, for example, dendritic cells, macrophages and B cells. Importantly for transplant rejection pathophysiology, both class I and II HLA

can be expressed by vascular endothelial cells.9 Most rejection responses are thought to be due to differences in HLA between donor and recipient, with the HLA mismatched antigens serving as the targets in antibody-mediated rejection. Non-HLA antigens may generate rejection responses but in general this is thought to be less common.1 There are important differences in HLA expression between T and B cells, which influence the interpretation of the crossmatch. T cells do not constitutively express HLA class II so the result of a T-cell crossmatch generally reflects antibodies to HLA class I only. B cells on the other hand express both HLA class I and II so a positive B-cell crossmatch may be due to antibodies directed against HLA class I or II or both. Hence, if the T- and B-cell crossmatches are positive the interpretation is that there may be either single or multiple HLA class I DSAb/s or a mixture of HLA class I and II DSAbs.