The same broad protective specificity was shown by mAb 2G8, a laminarin-recognizing, anti-b-glucan IgG2b monoclonal antibody, which was able to control infections by C. albicans and C. neoformans.. As for other promising antifungal vaccines and antibodies, however, details of the antigenic determinants and effector mechanisms of the protective immunity provided by the b-glucan-based vaccine and anti- bglucan mAbs remain largely elusive. In this paper, we have tried to gain insights into the mechanisms of protection induced by anti-b-glucan antibodies by comparing the anti-b-glucan mAb 2G8 with a mAb which has equal sequences of light and heavy chain Complementarity Determining Regions as the IgG, but is of different isotype. C. albicans, the most widespread agent of fungal disease in humans, has been used as a test model in our investigations. We considered that b-glucan is often secreted by fungi in association with cell wall proteins, in particular the mannoproteins, and that several cell wall proteins which are secreted into the external Pancuronium dibromide milieau are known to be covalently linked to b-glucan. Thus, the secreted material was Butenafine hydrochloride analyzed by SDS-PAGE and Western blot to identify possible, discrete protein components bearing mAb-reactive motifs. As shown in Fig 5, abundant IgG-reactive material was indeed detected in both hyphal and yeast secretion. For its highly heterogeneous and polydisperse appearance this material likely consisted mostly of molecularly ill-defined, variously sized polysaccharides. Nonetheless, a number IgG-reactive bands, in particular three bands with an approximate molecular weight of 165, 157 and 138 kilodaltons, were coarsely distinguishable within the smear. Apparently similar mAb 2G8-reactive, faint bands were also detected among cell wall proteins extracted by SDS- or b–glucanase treatment from isolated fungal cell wall, suggesting that the IgG-reactive, secreted proteins originated from fungal cell wall. None of the components present in the secretory material or in the cell wall protein extracts was recognized by the IgM mAb. As expected from the abundance of mannoproteins in the culture supernatant and the sensitivity of their mannan component to periodate oxidation, the secretory material was also very reactive with Concanavalin A, a reactivity that was completely lost upon periodate treatment. Oxidation also affected some IgG mAb-reactive constituents, but it left completely intact other components, inclusive of those corresponding to the 157 and 138 kDal bands, in keeping with the expected resistance of b1,3 glucan to periodate oxidation. By immuno-affinity purification onto a mAb 2G8-Protein ASepharose column, the IgG mAb-reactive material was isolated from culture supernatants yielding a fraction that comprised at least two of the reactive bands observed in total fungal secretion, in particular the component with an apparent molecular weight of 138 kDal. Interestingly, this fraction was also recognized by sera from mice immunized with the Lam-CRM vaccine, suggesting that at least some of the anti-b-glucan antibodies generated by this protective vaccination have the same specificity as the protective IgG mAb. To gain insights into protein constituents associated with the IgG-reactive, secreted b-glucan, the two bands of 138 and 157 kDal, best recognizable in the fungal secretion, were excised from the gels, subjected to controlled proteolysis with trypsin and analyzed by mass spectrometry.