Background Antibodies are the main effectors against malaria blood-stage parasites. shown that overall polyethylene glycol purification of human being serum/plasma samples and protein G Sepharose purification of rabbit sera are ideal for recovering practical Ag-specific antibodies. Summary Consequently, critical thought of the purification method is required to avoid selecting non-representative populations of recovered Ig, which could influence interpretations of vaccine effectiveness, or impact the search for immune correlates of safety. Background Serological analysis of humoral reactions is vital for vaccine evaluation as well as epidemiological studies for recognition of immune correlates. For both in vivo (when passively transferred) and in vitro applications, immunoglobulins need to be purified in order to not only get rid of potential pathogens but also to remove nonspecific effects of other serum components such as match, oxidative radicals, cytokines and drugs. Depending on the application, standard purification protocols are either geared towards large level purifications under GMP-conditions of polyclonal Ab from immune individuals [1-4] or towards isolation of monoclonal Ab from either biological fluids or culture supernatant for basic research study or passive immunotherapy [5-8]. The majority of methods described in the literature are based either on binding to certain subclasses of immunoglobulins (Igs) by BAY 63-2521 molecules such as Protein A and G [7] or on precipitating proteins in the size range of Igs with reagents such as ammonium sulfate, (NH4)2SO4, [6], caprylic acid/(NH4)2SO4 [9] or polyethylene glycol (PEG) [10,11]. Some methods C here the exception being (NH4)2SO4 and PEG protocols C require an acidic condition between pH 2C4 which can have a negative impact on the quality, integrity and function of the purified antibody molecules. In addition, the efficiencies of recovering a representative pool of antibodies can vary by method.(e.g. for human Igs Protein A binds preferentially BAY 63-2521 to IgM and IgG isotypes, but not to the IgG3 subclass). This is of particular interest for disease models in which IgG3 functions as a marker of exposure, such as in protozoan infections [12-14] as well as for the mounting evidence that blood-stage specific IgG3 may be associated with protective immunity against malaria depending on the target antigen [15-17]. In addition, IgG3 has been shown to be the most efficient Ig isotype in mediating antibody-dependent cellular inhibition (ADCI) at least in vitro [18]. Comparable selectivity for isotypes DNMT has been reported for murine as well as rat antibodies. Igs from some species do not purify at all when using Protein A or G [19]. Very limited information is available in the literature on how the integrity and functional activity of antibodies are affected by various purification methods; thus, a formal comparison is needed to evaluate any differences. One major focus point in malaria vaccine development is the analysis of immune responses against the blood stage parasite of Plasmodium falciparum. Thus, model systems were established based on sera from rabbits immunized with a recombinant 42 kDa C-terminal portion of Merozoite Surface Protein 1 (MSP-1p42) and plasma/serum from malaria-exposed residents and respective malaria-na?ve rabbit- and human control sera. The methods BAY 63-2521 chosen for comparison were: (a) depletion of serum proteins by caprylic acid followed by precipitation of Ig using (NH4)2SO4, designated CA-AS; (b) enrichment of Ig using PEG; (c) specific binding of IgG using Protein G Sepharose; and (4) specific binding of IgM and IgG isotypes using Sepharose coupled with Protein A/G. The recovery from each method was determined by UV spectrophotometry and by Ag-specific ELISAs. The integrity of each Ig preparation was tested by SDS-gel electrophoresis and the ability of the isolated Ig to bind to their specific antigen (Ag) was measured in MSP-1p42 specific ELISAs. Potential changes in the Ag-specific titer, isotype distribution and Ab avidity were also determined by ELISA. Lastly, conservation of biological function of purified Ig after separation with the respective methods was tested by in vitro parasite growth inhibition assays (GIA). This led to the observation.