How we wish to be cited:
Brandt L. Vitamin B12 and phagocytosis [evaluation]. Rondel 2005; 25. URL: http://www.rondellen.net

 Intellectual environment

 Following an appointment at the Department of  Bacteriology, Lund University,  I got the opportunity to work at the Department of Internal Medicine, University Hospital of Lund, in the beginning of the 1960´s.

I soon became involved in activities led by the dynamic internist Åke Nordén, who several years later made fundamental contributions towards organisation and research within Swedish primary health care, the so called ´Dalby project´.

Nordén had great knowledge about microbiology. He had in the 50´s made important contributions in mycotic infections (sporotrichosis) and had also isolated a previously unknown mycobacterium  causing granulomatous skin lesions in swimming hall visitors.

Besides an extensive clinical competence Nordén was greatly interested in laboratory work and had equipped a laboratory for hematologic activities. Among other things serum vitamin B12 could be determined in cultures of Euglena gracilis. Some doctors and students met regularly in the laboratory. Methods and research results were discussed and new projects were started.

How to measure leukocyte phagocytosis

One new project was to study the phagocytic activity of neutrophilic leukocytes in various hematologic disorders. A standardized in vitro method was then necessary. It seemed most logic to use bacteria as ”food” for the neutrophils. This, however, turned out to be unpractical.  Bacteria are small and each neutrophil could ingest a lot of them making it almost impossible to count the number of bacteria phagocytosed per cell.

An article in a journal of virology was helpful. The authors had studied the effect of influenza virus on phagocytosis by neutrophilic leukocytes. As ”food” they used heat killed baker´s yeast. Their method was adopted and now it turned out that in our hands the number of yeast cells ingested varied between 0-8 per neutrophil.  Their size was relatively large and reasonably uniform. They had a light blue colour in ordinary hematologic stainings and could be easily counted in each cell.

An in vitro method was elaborated to assure a constant relation between the number of yeast cells and the number of neutrophils in the experiments (1). Initially the main interest was directed towards the function of the neutrophils in the chronic myeloproliferative disorders chronic myeloid leukemia, polycythemia vera, essential thrombocytemia and myelofibrosis. Interesting differences were observed  but will not be described here.

Vitamin B12 and phogocytosis

The characteristic blood picture associated with severe vitamin B12 deficiency, pernicious anemia (PA), also deserved special attention. In addition to macrocytic anemia, neutropenia with hypersegmented nuclei are typical findings. It was known that even severe infections in PA patients were not always associated with leukocytosis and experimental studies had shown that injections with endotoxin did not cause the leukocytosis expected.

It now turned out that the neutrophils, constituting  a minority with a remarkable appearence, also had a poor appetite. Their phagocytic capacity was significantly reduced  compared with the corresponding cells from healthy persons. The activity was not improved when vitamin B12 was added to their environment in vitro. Daily subcutaneous injections of cyanocobalamin were associated with increasing numbers of circulating neutrophils beginning after 5-10 days and with a coincident improvement of the phagocytic activity. A few days later the hypersegmentation was not apparent. The pattern described was similar in 11 consecutive patients with PA. In one patient with severe anemia and neutropenia due to a laboratory verified deficiency in folate an identical response was observed following daily injections of 0.2 mg folic acid.

Discussion and conclusion

It is reasonable to assume that a deficiency in vitamin B12, in addition to several other problems, may contribute to an impaired cellular defence against infections. The above results only demonstrated a reduced capacity of neutrophilic leukocytes to take up foreign material in patients with PA. Of course the killing of ingested bacteria is the definitive success for a neutrophilic leukocyte. It is therefore interesting that later studies have shown that the killing of bacteria by such cells is ineffective in patients with severe vitamin B12 deficiency (2).

Dr Lars Brandt
Persikevägen 47
SE-223 55 Lund, Sweden
E-mail: lars.brandt@mbox305.swipnet.se

References

1.      Brandt L. Studies on the phagocytic activity of neutrophilic leukocytes. With special reference to chronic myeloproliferative disorders and megaloblastic anemia. Scand J Haematol. Suppl. No. 2. Copenhagen: Munksgaard 1967.

2.      Skacel P O, Chanarin I. Impaired chemoluminescence and bacterial killing by neutrophils from patients with severe cobalamin deficiency. Br J Haematol 1983; 55: 203-15.

Published November 27, 2005