236
6 Immunoproteins
coproteins which, as the result of partial hydrolysis, have lost their protective sialic acid residues
[42, 166, 167, 200].
6.S Humoral Defence in Invertebrates
The invertebrates have no system equivalent to
the complex immune system of the vertebrates.
Nevertheless, the interior of the invertebrate
body is just as sterile as that of vertebrates,
although the danger of microbial contamination
is just as great. They must also have mechanisms
for distinguishing self and non-self, although we
know next to nothing about these. In the case of
invertebrate animals, one can also differentiate
between cellular and humoral defence mechanisms. The most important cellular mechanisms
are phagocytosis and the encapsulation of foreign
cells and organisms. The humoral defence components of the invertebrates encompass the cellagglutinating agglutinins (Iectins), the cell-wallperforating lysins [24, 150], and lysozyme, which
has the capacity to dissolve the cell walls of many
bacteria. Humoral defence mechanisms are particularly well developed in the annelids, arthropods, molluscs and echinoderms. Of the three
groups of defence substances, lectins have
already been discussed, and the lysozymes will be
dealt with in Chapter 13. Lysins have been
detected in many representatives of the animal
groups mentioned but have been little characterized biochemically. Detailed studies of humoral
defence have been carried out for only a few
insects and annelids [17, 44, 110].
Amongst the insects, the giant diapause pupa
of the moth Hyalophora cecropia has received
particular attention. With a body weight of up to
10 g, this provides ca. 1-2 ml of haemolymph.
Treatment with living, non-pathogenic, or killed
pathogenic bacteria strongly enhances the bactericidal activity of the haemolymph over several
days. The expression of immunoprotein genes in
the fat bodies is increased, whilst that of the other
genes remains at basal levels. This response has
allowed the isolation from the haemolymph of no
fewer than 15 proteins which are involved in
humoral defence; the cDNA or gene sequences
have been determined for several of them. These
antibacterial proteins are distributed amongst
three families: the small cecropins (3-5 kDa) , the
larger attacins (20 kDa), and lysozyme. The
whole system becomes especially important at the
end of the pupal resting phase when histolysis
begins and bacteria from the gut cavity may enter
the haemolymph. The induction of antibacterial
proteins occurs in the Lepidoptera, Diptera and
Hymenoptera, i.e. in all highly developed insect
orders. Amongst the proteins induced by bacteria
are several which have no direct antibacterial
effect, e.g. the 48-kDa protein P4, which is the
major protein induced in H. cecropia [86, 180].
The cecropins are polypeptide chains of 35-37
amino acids with a basic N-terminus and a nonpolar C-terminal region. The C-terminal amino
acid carries an amide group formed from the terminal glycine of the primary translation product.
The prepro-cecropins possess a signal sequence of
22 amino acids and a pro-sequence of 2-4 amino
acids, both of which are absent from the mature
protein. Three cecropins (A, B and D) are known
from H. cecropia to kill and partially lyse both
Gram-negative and Gram-positive bacteria.
Comparisons of protein and gene sequences show
that the antibacterial proteins of many Lepidoptera and Diptera are homologues of cecropin,
even though only five amino acids are conserved.
Some of these proteins received various other
names from their discoverers: "lepidopterans A
and B" in the lepidopterans Manduca sexta,
Antheraea pernyi and Bombyx mori; and "sarcotoxins lA, IE and IC" in the dipterans Sarcophaga peregrina and Drosophila melanogaster.
There was even a recent report of a cecropin in
porcine gut tissue, indicating that these peptides
are widely distributed in the animal kingdom
[62, 85, 86, 96, 117].
H. cecropia possesses two forms of attacin, one
basic and one acidic, encoded by different genes;
they agree in 79 % of their 1844 amino acids. Like
the cecropins, the attacins are also synthesized as
a prepro-protein. They are specific for Gramnegative bacteria. A homologous protein has
been detected in M. sexta via cDNA cloning. The
attacins belong to the same family as the sarcotoxins IIA, lIB and IIC from S. peregrina; the sarcotoxin sequence of 270 amino acids is 20 % similar to that of the attacins [86, 181]. A third family
of antibacterial insect proteins includes the three
diptericins from the fly Phormia terranovae. The
predominant form is a polypeptide of 82 amino
acids with an amidated C-terminus, but it has no
sequence similarity to either the cecropins or
attacins. The subsidiary forms are highly homologous. The diptericins are also specific for Gramnegative bacteria [41, 86, 197]. Sequence similarity to the diptericins is shown by four antibacterial
proteins which appear in the haemolymph of the
honeybee Apis melli/era after the injection of
6 Immunoproteins
coproteins which, as the result of partial hydrolysis, have lost their protective sialic acid residues
[42, 166, 167, 200].
6.S Humoral Defence in Invertebrates
The invertebrates have no system equivalent to
the complex immune system of the vertebrates.
Nevertheless, the interior of the invertebrate
body is just as sterile as that of vertebrates,
although the danger of microbial contamination
is just as great. They must also have mechanisms
for distinguishing self and non-self, although we
know next to nothing about these. In the case of
invertebrate animals, one can also differentiate
between cellular and humoral defence mechanisms. The most important cellular mechanisms
are phagocytosis and the encapsulation of foreign
cells and organisms. The humoral defence components of the invertebrates encompass the cellagglutinating agglutinins (Iectins), the cell-wallperforating lysins [24, 150], and lysozyme, which
has the capacity to dissolve the cell walls of many
bacteria. Humoral defence mechanisms are particularly well developed in the annelids, arthropods, molluscs and echinoderms. Of the three
groups of defence substances, lectins have
already been discussed, and the lysozymes will be
dealt with in Chapter 13. Lysins have been
detected in many representatives of the animal
groups mentioned but have been little characterized biochemically. Detailed studies of humoral
defence have been carried out for only a few
insects and annelids [17, 44, 110].
Amongst the insects, the giant diapause pupa
of the moth Hyalophora cecropia has received
particular attention. With a body weight of up to
10 g, this provides ca. 1-2 ml of haemolymph.
Treatment with living, non-pathogenic, or killed
pathogenic bacteria strongly enhances the bactericidal activity of the haemolymph over several
days. The expression of immunoprotein genes in
the fat bodies is increased, whilst that of the other
genes remains at basal levels. This response has
allowed the isolation from the haemolymph of no
fewer than 15 proteins which are involved in
humoral defence; the cDNA or gene sequences
have been determined for several of them. These
antibacterial proteins are distributed amongst
three families: the small cecropins (3-5 kDa) , the
larger attacins (20 kDa), and lysozyme. The
whole system becomes especially important at the
end of the pupal resting phase when histolysis
begins and bacteria from the gut cavity may enter
the haemolymph. The induction of antibacterial
proteins occurs in the Lepidoptera, Diptera and
Hymenoptera, i.e. in all highly developed insect
orders. Amongst the proteins induced by bacteria
are several which have no direct antibacterial
effect, e.g. the 48-kDa protein P4, which is the
major protein induced in H. cecropia [86, 180].
The cecropins are polypeptide chains of 35-37
amino acids with a basic N-terminus and a nonpolar C-terminal region. The C-terminal amino
acid carries an amide group formed from the terminal glycine of the primary translation product.
The prepro-cecropins possess a signal sequence of
22 amino acids and a pro-sequence of 2-4 amino
acids, both of which are absent from the mature
protein. Three cecropins (A, B and D) are known
from H. cecropia to kill and partially lyse both
Gram-negative and Gram-positive bacteria.
Comparisons of protein and gene sequences show
that the antibacterial proteins of many Lepidoptera and Diptera are homologues of cecropin,
even though only five amino acids are conserved.
Some of these proteins received various other
names from their discoverers: "lepidopterans A
and B" in the lepidopterans Manduca sexta,
Antheraea pernyi and Bombyx mori; and "sarcotoxins lA, IE and IC" in the dipterans Sarcophaga peregrina and Drosophila melanogaster.
There was even a recent report of a cecropin in
porcine gut tissue, indicating that these peptides
are widely distributed in the animal kingdom
[62, 85, 86, 96, 117].
H. cecropia possesses two forms of attacin, one
basic and one acidic, encoded by different genes;
they agree in 79 % of their 1844 amino acids. Like
the cecropins, the attacins are also synthesized as
a prepro-protein. They are specific for Gramnegative bacteria. A homologous protein has
been detected in M. sexta via cDNA cloning. The
attacins belong to the same family as the sarcotoxins IIA, lIB and IIC from S. peregrina; the sarcotoxin sequence of 270 amino acids is 20 % similar to that of the attacins [86, 181]. A third family
of antibacterial insect proteins includes the three
diptericins from the fly Phormia terranovae. The
predominant form is a polypeptide of 82 amino
acids with an amidated C-terminus, but it has no
sequence similarity to either the cecropins or
attacins. The subsidiary forms are highly homologous. The diptericins are also specific for Gramnegative bacteria [41, 86, 197]. Sequence similarity to the diptericins is shown by four antibacterial
proteins which appear in the haemolymph of the
honeybee Apis melli/era after the injection of