Microbial

Pathogenesis

1990;

Anti-adhesive

activity

of human casein against pneumoniae and Haemophihs

Streptococcus influenzae Gustav Aniansson,” Catharina Svanborg Department Goteborg,

of Clinical Sweden

(Received

November

8: 315-323

Bengt

Immunology,

Andersson,

University

1, 1989; accepted

Ragnar

of Goteborg,

Lindstedt

Guldhedsgatan

in revised form January

1990;

10, 473

46

31,199O)

Aniansson, G. (Dept of Clinical Immunology, University of Goteborg, 46 Goteborg, Sweden), 0. Andersson, R. Lindstedt and C. Svanborg. human casein against Streptococcus pneumoniae and Haemophilus Pathogenesis

and

Guldhedsgatan Anti-adhesive influenzae.

10, 413 activity of Microbial

8: 315-323.

The casein

fraction of human milk was found to inhibit the attachment of Streptococcus and Haemophilus influenzae human respiratory tract epithelial cells. The inhibitory activity for S. pneumoniae remained after heat and trypsin treatment of the casein and was found in oligosaccharides released from casein. rc-Casein, which is the most highly glycosylated casein component, inhibited pneumococcal attachment at concentrations similar to the whole casein fraction. The results are consistent with the known recognition of GlcNAc~l-3Gal by S. pneumoniae, since human milk and bovine colostrum, which contain GlcNAc, inhibited attachment, but mature bovine milk lacking GlcNAc did not. The effect on H. influenzae was similar to that on S. pneumoniae in that the attachment was inhibited by human casein and bovine colostrum, but not by either mature bovine milk or by the bovine casein fraction. The K-casein component of human milk was a less efficient inhibitor of H. influenzae attachment than the whole casein fraction and the free oligosaccharides were inactive. This anti-microbial effect of human casein represents a new mechanism for the protection by breast-milk against respiratory tract infection. pneumoniae

Key

adhesion;

words:

casein; breast-milk;

respiratory

tract infections

Introduction Glycoconjugates interact specifically with microbial lectins, e.g. viral envelope proteins, bacterial adhesins and toxins.’ The specificity is provided by saccharide sequences, e.g. the GM, ganglioside recognized by cholera toxin,2,3 Gala1 -4Gal/? by uropathogenic E. CO/~~,~ or GlcNAr$l -3Gal by S. pneumoniae.6 When membrane bound, the glycoconjugates act as receptors, and the interaction with, for example, bacteria results secreted these oligosaccharide in attachment to the receptor-bearing cell. ’ When sequences have other functions. For example, the presence in external secretions of oligosaccharide sequences corresponding to the cell-bound receptors, provides the to epithelial basis for competitive inhibition of microbial binding. a Since attachment

* Author of Clinical

to whom correspondence Immunology, Salvegatan

0882-401

O/90/05031

5+09

$03.00/O

and reprint requests should 23, 223 62 Lund, Sweden.

be addressed:

Gustaf @ 1990

Aniansson, Academic

Department Press Limited

G. Aniansson

316

et al.

ceils is an important event in the pathogenesis of many bacterial infections, inhibition of attachment by secreted oligosaccharides may protect against infection.* Human milk is a rich source of free oligosaccharides and glycoconjugates.‘,” Human milk.inhibits the attachment both of S. pneumoniae and H. influenzae to nasopharyngeal epithelial cells in vitro.8 Inhibitors for pneumococcal binding were identified in the free oligosaccharide fraction, as expected from its content of lacto- and neolactotetraose, with known receptor activity for pneumococci.’ Additional components with a molecular weight greater than 5 kDa but not of an immunoglobulin nature were also shown to interact with both H. influenzae and S. pneumoniae.* The present study identifies casein as the anti-adhesive non-immunoglobulin component in the high molecular weight fraction of human milk.

Results Anti-adhesive effect of human milk casein The attachment of S. pneumoniae (CCUG 3114) and H. influenzae (Hi 198) to human nasopharyngeal epithelial cells was inhibited by mature human milk and bovine colostrum but not by bovine milk (Table 1, Fig. 1). The nature of the inhibitory component(s) in human milk was first analysed by separation according to molecular weight. The high molecular weight fraction inhibited

Table 1

Adhesion

inhibition

by human

and bovine Bacteria/cell

milk (% of saline

control)

S. pneumoniae

H. influenzae -~-

Inhibitor Saline control Mature milk, bovine Mature milk, human HMWF,‘human LMWF,‘human

(%)

P

Mean

W)

51 55 8

(100) (108)

-NS

98 86

(100) (88)

29 42

(30) (43)

92

(94)

(16) (12) (‘31)

6 31

‘Compared with saline *High molecular weight ’ Low molecular weight

control: fraction fraction

see Materials (>5 kDa). ( < 5 kDa).

Fig.

1.

Inhibition by bovine

of the attachment colostrum.