Western blots were probed using murine sera raised to recombinant proteins based on the individual MSP1 block 2 types [11] and [15]. Bound antibody was detected with horseradish peroxidase-conjugated rabbit anti-mouse secondary antibody

(DAKO), and bands visualized using 5 ml per blot of stabilized TMB (3,3′,5,5′-tetramethylbenzidine) substrate (Promega, UK). Groups of five CD-1 outbred mice were immunized (Northwick Park Institute for Medical Research, UK) with each antigen formulated in the ImjectAlum adjuvant (Perbio Science, Cheshire, UK). Each polyvalent hybrid protein was diluted with PI3K inhibitor phosphate-buffered saline (PBS) to a concentration of 1 mg ml−1, and 3 volumes of Imject Alum KU-55933 concentration added and allowed to mix for 30 min at room temperature. Each antigen–adjuvant mixture was administered intra-peritoneally, each mouse receiving 50 μg protein per dose in a final volume of 200 μl. Three doses were administered

at monthly intervals, and blood was collected before immunization and 2 weeks after each dose (on days 14, 42, and 70). The purified polyvalent hybrid antigen (+)T-K1SR-R033-Wellcome (antigen 6, Fig. 1A) was used to immunize New Zealand white rabbits (Pettingill Technology Limited, UK). Five rabbits received 200 μg of purified protein intramuscularly Vasopressin Receptor at days 0, 14, 28, 42, 56 and 70 following a 77 day protocol with one rabbit receiving adjuvant with PBS only as a control (Freund’s complete adjuvant was used on day 0 immunization, Freund’s incomplete adjuvant for boosting immunizations). Test bleeds were taken on days 35, 49 and 63, final bleeds were collected on day 77. Ten P. falciparum isolates were

cultured, including 6 with K1-like MSP1 block 2 sequences (3D7, T9/96, T9/102, D6, K1, Palo Alto), 3 with MAD20-like block 2 sequences (Wellcome, MAD20, Dd2), and R033 representing the R033-like block 2 type that has minimal subtypic polymorphism. Each was identified and discriminated by sequencing of MSP1 block 2. Parasite cultures were grown under standard conditions to a parasitemia of 4–10% (predominantly schizont stage although asynchronous) and cells washed twice after centrifugation before resuspension in PBS/1% BSA, for preparation of IFA slides. Specific antibody reactivities to each of the parasite isolates were assessed following previously described methods [22]. Parasites were air-dried onto multiwell IFA slides (Hendley, Essex, UK), fixed with 4% formaldehyde and tested with serial doubling dilutions of murine sera (1/50 to 1/409,600) in PBS with 1% bovine serum albumin (15 μl/well) and incubated for 30 min. Biotinylated anti-mouse or anti-rabbit IgG (Vector Laboratories Inc.