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Anti-streptococcal T4 titres in human sera tend to be higher in normal sera of the Hp type hp 2-2 than in normal sera of hp 2-1 subjects. If the sera are heated above a temperature of 50 degrees C the difference disappeared and the titres are reduced. When heating sera to 63 degrees for 10 min no agglutination activity for T4 streptococci can be observed.

By testing 167 human sera a surprising dimorphism could be found. All sera of the haptoglobin type hp 1-1 belong to the group with an anti-G streptococci titer in the range of 1:0 to 1:10 whereas sera of the types hp 2-1 and hp 2-2 do have titers in the range between 1:200 and 1:3200 or more. All tests are carried out in the double blind technique.

The antibody-like activity of haptoglobin types hp 2-2 and hp 2-1 for streptococci having the T4 antigen is not reduced by saturation with hemoglobin.

The relationship between haptoglobin type and the agglutinability of some group G streptococci, which was observed in humans, could also be demonstrated in animal sera. In humans the haptoglobin type Hp 1-1 is correlated with a lacking or very low agglutinability. Sera of 10 rhesus monkeys showed Hp-type 1-1 and agglutinated the streptococci only to dilutions of the serum up to 1:4. The sera of 48 pigs contained an Hp 1-1 like type and a streptococcus agglutination titer of max. 1:10. Seven ahaptoglobinaemic sera gave the same values. Fifty examined sera of rabbits showed also an Hp 1-1 like pattern and did not agglutinate or in undiluted state only.

Human sera are able to agglutinate latex particles sensitized with antihaptoglobin serum produced from sheep. The agglutination depends on the haptoglobin types. Similar to the agglutination of T4-streptococci the titer of Hp 1-1 is very low and the titers of sera of the types Hp 2-1 and Hp 2-2 are 1:160 or higher.

A relationship was found between the haptoglobin types of human sera and the agglutinability of some strains of group G streptococci. Sera with the haptoglobin types Hp 2-2 and Hp 2-1 agglutinate these streptococci to high titers, from 1:200 up to more than 1:6400. On the other hand, the sera with haptoglobin type Hp 1-1 agglutinate not more than up to titers of 1:16 (mostly lower). Out of 102 strains of group G streptococci only 3 showed this characteristic phenomenon. This study was undertaken in order to elucidate whether the Hp 2-2 and Hp 2-1 proteins have antibody activity. Incubation of Hp 2-2 or Hp 2-1 sera with antihaptoglobin antisera or with anti-Hp 2-antiserum did not change the agglutinating activity but the haptoglobin was eliminated from the sera. Absorption of Hp 2-2 and Hp 2-1 sera with these group G streptococci lowered the titers significantly but the haptoglobins are detectable as in the non-absorbed sera. Sera with haptoglobin 1-1 contain an inhibitor. Mixing of Hp 2-2 and Hp 2-1 sera with high agglutinating titers with Hp 1-1 sera (low titers) was followed by a significant decrease of the titer.

Sera of 157 baboons (Papio hamadryas and P. anubis) 21 chimpanzees (Pan troglodytes) five orang utans (Pongo pygmaeus) three mountain gorillas (Gorilla gorilla beringei) and three gibbons (Hylobates lar lar) were examined for the content of antistreptolysin O, antidesoxyribonuclease B, for the presence of rheumatoid factors as well as for the level and type of haptoglobin. The mean antistreptolysin O titer (AST) in baboons was 106 ASU +/- 18 in dextransulfate absorbed sera ("real" AST) and 182 ASU +/- 34 in non-absorbed sera. The mean decrease after absorption was 20% (i.e., 20% inhibitor + 80% antistreptolysin O), a value that is lower than previously found in rhesus monkeys (55%) or in man (40%). Raised values of anti-DNase B were found in two baboons only, and none of the sera of that species displayed presence of rheumatoid factors. In chimpanzees, the mean AST was 68 +/- 29 in absorbed and 87 ASU +/- 57 in non-absorbed sera. Anti-DNase B was raised in three animals, and in two cases the increase was correlated with raised AST. Of 19 chimpanzee sera examined, 13 were found to contain antigammaglobulins ("rheumatoid factors") the titers of which reached 1:64 or more. All primate sera tested so far showed haptoglobin type 1-1 or Hp 1-1-like patterns. The haptoglobin level in chimpanzees and baboons was comparable to that established in man; in rhesus monkey, on the other hand, much lower values (40-62 mg/100 ml) or ahaptoglobinemia were observed. The sera of all monkeys and apes tested so far showed a very low (undiluted, or up to 1:10 titer at most) agglutinating activity against T4-antigen-carrying streptococci. This is in agreement with our observations made previously which indicated that human or animal sera of haptoglobin type 1-1 agglutinated streptococci to a much lower degree than type Hp 2-2 or type Hp 2-1 sera.

The haptoglobins in man and in mammals are agglutinin-like-substances for streptococci having the T4 antigen. The kind of the agglutinin-like behaviour depends on the genetic type of the haptoglobins. Haptoglobins of the types Hp 2-2, Hp 2-2 like and Hp 2-1 are hightitred complete agglutinins (titre in the range between 1:200 up to 1:3000 and higher) whereas haptoglobins of the type Hp 1-1 are "blocking antibodies". - The steps of the discovery and evidence are presented in detail. Different questions dealing with the clinical significance are discussed.

The relationship between haptoglobin type and titer of agglutination against streptococci carrying the T4-antigen was examined in 100 pairs of sera (mother/child). In healthy pregnant women high titers were predominant in individuals of haptoglobin type 2--2. Lower titers were found in sera of women with diseases during pregnancy. In 4% of the newborns only the haptoglobin type could be recognized. In comparison of maternal and neonate titers of agglutination pointed out the antibody-like activity of haptoglobins.

A significant correlation was found between levels of haptoglobin in sera from Indonesian patients with tuberculosis and the extent to which these sera suppressed mitogen-driven activation of normal lymphocytes in vitro. As in a previous study we showed that there was an inverse relationship between haptoglobin levels and the circulating lymphocyte count in the same group of patients, it is now suggested that this protein has an immunoregulatory role in tuberculosis. Similar observations have been made by other workers on patients with cancer. There was no difference in the distribution of the 3 allotypes of haptoglobin in patients and healthy subjects nor was there any association between such allotypes and the lymphocyte count, the dermal reactivity to tuberculin or the degree of suppression.

In systematic investigations we found a relationship between the haptoglobin types of human sera and the agglutinability of some group-G streptococcal strains. Sera with the haptoglobin type Hp 1-1 do not agglutinate these strains (or with low titres up to 1:16 only). On the other hand sera with the haptoglobin types Hp 2-1 or Hp 2-2 agglutinate the streptococci with titres from 1:200 to 1:3,200 (or more). The aspects resulting from these findings were discussed in detail. They may have among others practical consequences for the forensic medicine and the role of the haptoglobins must be thought over again.

The haptoglobins in man and in mammals react with streptococci bearing the T4-antigen. Hp 2-2 and Hp 2-1 react with high titres like complete agglutinins while Hp 1-1 acts like a blocking antibody. It is surprising to observe the similarity of the behaviour of the haptoglobins and of IgG and IgM. Streptococci carrying Hp 1-1 yield a positive Coombs-test. The Coombs-serum however, is an anti-human-haptoglobin-body from sheep. By means of supplements it has been possible to increase partly considerably the titres of Hp 2-1 and Hp 2-2 against the streptococci.

Some strains of beta-haemolytic streptococci were agglutinated with high titers (1:200-1:6400) by human sera of the haptoglobin types 2-2 and 2-1. No agglutination or with low titers (up to 1:20) was observed with sera of the haptoglobin type 1-1. This reactivity depends from the contents of Streptococcus pyogenes T-antigens of the T-complex 4,24... This T4-antigen is present in group A streptococci (Strep. pyogenes) of the types 4, 24, 26, 28, 29, 46, 48 and 60 but it may be present also in some strains of streptococcal groups C and G. During a 10-year period we isolated 12 strains of Strep. equisimilis (group C) carrying the T-4 antigen (1.6%) and 50 group-G streptococci with T-4 antigen (6.4%) of all group G streptococci). These strains were agglutinated without an exception with high titers by Hp 2-2 and Hp 2-1 sera but not by sera of the haptoglobin type 1-1. The same particuliarity was shown by Streptococcus pyogenes types of the T-complex 4, 24... One strain of type 26 (BC 179) has no T antigen and therefore it was not agglutinated in the above mentioned manner. The phenomenon depends from the medium; it occurs after cultivation of the streptococci in Pope broth or in meat-infusion with glucose but not or only reduced in beef heart-proteose-medium. The agglutination reaction is caused by the haptoglobin but not by agglutinins against the T4-antigens.

The median level of haptoglobin types 2-2 and 2-1 was found to be proportional to the agglutination titer of T4 antigen-carrying streptococci (Fig. 1). This relationship need not exist in individual sera since, as seen from Table 1, high agglutination titers may be caused by sera with low levels of haptoglobin. Thus the agglutination reaction might depend not only on the quantity of haptoglobin but also on other factor(s) (at least in individual serum samples). - On the other hand, different agglutination titers did not correlate with the quantity of T4 antigen either. A strain of Strep. pyogenes, type 60, was agglutinated at high titers by sera with a high level of haptoglobin in spite of its low ability to absorb haptoglobin. This was in contrast to a strain of group G (20488) which had a high capacity both to become agglutinated and to absorb haptoglobin (Table 2). Absorption of haptoglobin by affinity chromatography decreased the agglutination titer for T4 streptococci. - The reaction between haptoglobin and T4-streptocci did not fix complement. No differences were found between sera of haptoglobin types 1-1, 2-1, and 2-2 with respect to the amount of C, C3, C4, and C3A, respectively (Tables 3-5).

The determinability of haptoglobin types is correlated with the titers of agglutination against streptococci carrying the T4 antigen. If the haptoglobin types in cord-sera cannot be determined (as a result of the physiological binding of haptoglobins) the agglutination reaction fails or the titers are greatly diminished. The dimorphism, which was found in sera of adults, can be demonstrated in cord sera, too, if they can be typed. It is concluded that the observed reaction between Hp 2-2 and Hp 2-1 sera with T4-streptococci is caused by the haptoglobin itself.