Antigenic specificity of a rabbit antiserum raised against the 15-28 segment of thymosin alpha 1

Structure and function of a thymic peptide is mimicked by Plasmodium falciparum peptides

Numerous Plasmodium falciparum antigens contain repetitive amino acid sequences. Two blood stage antigens, Pf11-1 and Pf332, were characterized in our laboratories and present high cross-reactivities, defining a family of cross-reacting antigens. In this report, we show that amino acid sequence homologies might explain these cross-reactivities, but that they extend to polypeptides from the host, namely thymosin-alpha 1 (T alpha 1). An antiserum raised in chickens and Saimiri monkeys against the synthetic Pf11-1 peptide cross-reacts with synthetic T alpha 1. Synthetic Pf11-1 and Pf332 peptides share some of the biological activities of T alpha 1. These results are discussed with respect to the mechanisms devised by malaria parasites for escape from the host immune response.

The identification of prothymosin alpha-like material in vertebrate lymphoid organs by a radioimmunoassay for the N-terminal decapeptide

A radioimmunoassay (RIA) is described for the detection and quantitation of prothymosin alpha (ProT alpha), and its N-terminal fragments containing as a minimum the first ten amino acid residues. This range of peptides includes thymosins alpha 1 (T alpha 1) and alpha 11 (T alpha 11). Antibodies against T alpha 1 and the tracer T alpha 1(1-10)Tyr11(125I), an analogue of the major epitope, were utilized in this RIA. 50% displacement of the ligand was observed with 1.3 pmol of T alpha 1 and 6.4 pmol of ProT alpha. The partially homologous parathymosin alpha (ParaT alpha) showed less than 2% crossreactivity with ProT A. Sephacryl S-200 gel filtration separation of the peptides of calf thymus, chicken spleen and trout spleen extracts prepared by a method eliminating proteolysis, combined with the above RIA, showed the presence of a major immunoreactive peak. Its elution volume corresponded to that of rat ProT alpha (apparent mol. weight 36,000) for both calf (37,000) and chicken (35,000) tissues. In trout it corresponded to a significantly higher molecular weight (62,000). No detectable levels of shorter fragments, including T alpha 1, were observed in any of the above species. The levels of ProT alpha-like peptides in calf thymus, chicken spleen and trout spleen were found to be 246, 8.6 and 7.7 micrograms respectively, of rat ProT alpha equivalents per gram of fresh tissue. The significance of the presence of ProT alpha-like polypeptides in vertebrate species as distant as fish and mammals, the absence of short T alpha 1-like fragments, and the relative conservation of the N-terminus as suggested by the RIA is discussed.