Liquidity Effects of Changes in a Pan-European Stock Index

Adding or deleting a security to or from an index can influence the share price considerably. A possible explanation that has been brought forward in the literature is the liquidity hypothesis according to which an increase in liquidity after an addition is responsible for the observed rise in value. In the following paper, we examine liquidity effects on securities that have been added to or deleted from the pan- European index STOXX 50 between 1998 and 2003, using bid-ask spreads as indicators for liquidity. While there is a medium term price effect, bid-ask spreads do not change significantly due to the index addition or deletion. Regression analysis shows that the explanatory power of bid- ask spreads for the observed price effect is negligible. As a consequence of our empirical findings, the liquidity hypothesis has to be rejected for the STOXX 50. This result, however, does not appear particularly surprising, as the STOXX 50 is composed of already highly liquid securities whose trading liquidity appears not to depend on membership in an international index. A possible explanation for the rejection of the liquidity hypothesis is that the applicability of the liquidity hypothesis hinges on the liquidity class of the stocks concerned before being added. Marginal increases of liquidity due to an index addition might decline with larger initial liquidity of the stocks added. Subsequent studies could focus on the particular shape of this 'liquidity curve' of stocks.Pan-European stock index, index effect, STOXX, liquidity, price effect

Tube leukocyte adherence inhibition assay : the assessment of tumor immunity in cancer patients and in rats

For the past two decades, intensive search has been made for the existence of tumor-specific antigens of human cancer. The recent succesful development of monoclonal antibodies against TAA on human cell membrane has not yet resulted in the identification of any tumor-specific determinant(s) on cancer cells. An alternative approach for the identification of tumor-specific antigens has been to study the immune response of the host to cancer. Cell-mediated cytotoxicity was initially investigated using microcytotoxicity assays (47). Specific cytotoxicity against a variety of cultured cells from human tumors was observed with lymphoid cells from tumor-bearers or individuals whose tumor had been resected. The whole concept of specific cell-mediated cytotoxicity in human cancer was doubted when natural cytotoxicity was discovered (18, 19). However, investigators working with the tumor extract-induced leukocyte adherence inhibition (LA I) phenomenon have successfully provided much of the existing evidence for specific anti-tumor immunity in animals and human cancers (81,82). The ultimate objective of the present study was to use the tube LA! assay to monitor the purification of human TAA from crude tumor extracts. On the assumption that T AA are foreign or modified human major histocompatibility complex antigens (HLA antigens) or are closely associated with these antigens, the biochemical techniques used to study the nature of HLA antigens could be applied to obtain an insight into the biochemical nature of TAA and their relation (if any) to HLA antigens. The tube LAI assay was chosen since it was claimed to be simple, rapid and reproducible. In the first instance it was necessary to develop a reliable tube LAI technique of high sensitivity. In the initial studies it was investigated whether this could be achieved by using partially purified tumor extracts. Since the amount of patient tumor material severely restricted the amount of crude extracts that could be chroma to graphed and purified further using other physico-chemical techniques, LAI studies in rats were also pursued